Issues with new heating zone

powerade

Sorry, I thought I responded to this earlier. The max output is 24 kw. When the boiler cut out this morning, Zone 1 temperature was 19.5 (thermostat set to 25 degrees) and Zone 2 temperature was 19.8 (thermostat set to 21 degrees). So yes, it is difficult to understand why it would cut out and why the temperature dipped to 48 degrees

John.G

powerade wrote: »

Sorry, I thought I responded to this earlier. The max output is 24 kw. When the boiler cut out this morning, Zone 1 temperature was 19.5 (thermostat set to 25 degrees) and Zone 2 temperature was 19.8 (thermostat set to 21 degrees). So yes, it is difficult to understand why it would cut out and why the temperature dipped to 48 degrees

Maybe the answer lies in a previous post #136....

"There were two consecutive system waiting periods which amounted to 8 minutes followed by one anti rapid cycle which was 2 to 3 minutes so the total off time was approx 11 minutes. 15 minutes later the temperature went up to 69 degrees again and the 11 minute off cycle kicked off again."

a waiting period is the time it takes the flow temperature to fall to its setpoint so one would expect the boiler to fire up again so did you mean that there was one waiting period of 4 minutes followed by another waiting period of 4 minutes (amounting to 8 minutes) without any boiler firing ? and did the first waiting period go off and was it immediately followed by another waiting period
of 4 minutes?. What I am trying (badly) to say is why do you get two waiting periods with nothing happening in between??. The only reason I can see is that the flow temperature had fallen to its set point (waiting time) before the 5 minute anti rapid cycle time had elapsed so another anti rapid cycle time was called for.

I still think you should be able to tune that boiler, maybe by reducing the anti cycle time to 2 to 3 minutes (if allowed) and see what happens, also maybe later try reducing the max output to say 12kw although it goes against the grain.

powerade

After the first waiting period the boiler fires up, the ch demands heat and the temperature shoots up to 69 degrees. This all happens in seconds. Then a second waiting period kicks off and the temperature drops to 60/61. Then it goes into a rapid anti cycle and that is when the temperature can really start to fall. I hate to say it but this pattern is not consistently repeated but I don't know if that has anything to do with messing around with the ABV setting.
I had an interesting visit from my plumber this evening. He confirmed that the radiators were not underspeced in Zone 2, that the Zone 1 valve was working fine, in spite of the LED not working, all heating controls were working fine and there is no dirt in the system. He balanced the system and flipped and cleaned the filter. He had no clue, however, about the Zone 2 heating issue or what was driving the rapid anti cycle. He did think, however, that the boiler was faulty as he witnessed the Zone 2 temperature rise issue and he is going to speak to WB tomorrow. I'm not convinced as all of the major boiler parts have been replaced but it won't do any harm. I couldnt really understand his explabation of the role of the ABV but said that he always sets it at .38. He offered no advice on TRVs in the context of the current heating issues.I also asked him about the pump head setting, the best I could get was that it shouldn't be set at 4. He was rushing to get off.
I am going to change the maximum CH output setting, as you suggest and I will see if I can reduce the anti cycle time.

John.G

That's a very detailed explanation, sorry for all the questions but after that second period of waiting does/did the boiler fire up again and shoot up to 69C and then go into anti rapid cycle or did it go straight from the second period of waiting onto anti rapid cycle?.

Re ABV, Generally speaking the ABV was set up to dissipate residual heat that build up in a heat exchanger when the boiler shuts down, not used much in oil boilers as the Hx in these which are basically a "box" contain 20 to 30 litres of water which will soak up the residual heat and won't cause a huge rise in temperature. A gas boiler Hx will only contain a few litres of water and are often made of aluminium so it was/is common practice each time the boiler cuts out to keep the circ pump running (pump overrun) for a couple of minutes, this, in itself is useless with the advent of zone valves and that is where the ABV comes in. Again traditionally circ pumps were fixed speed (constant curve) pumps that will have the highest head when pumping against a closed circuit and when the zone valve(s) or TRVs start opening then the pump head will start reducing. Bearing this in mind it was relatively easy to set up the ABV to only pass water when all the circuits were closed but once anyone opened then the ABV will close off. However because a lot of pumps are now run in constant pressure mode (like yours) then the ABV will have to be set up to by pass a fixed quantity of water continuously. Some gas boiler have a internal by pass (like yours) and generally don't need a ABV, some now also have have a stainless steel Hx and may not have a internal by pass and no pump overrun/ABV. It is also common practice to use one rad, say a towel rad without a TRV and with the flow connected upstream of any zone vave to act as a constant by pass and no ABV is fitted.
I know your ABV is on a very short piece of pipe but you said I think that even when you set it at index o.45 (4.5M) that the horizontal pipe was still roasting so ther is just a slight suspicion that this ABV is passing, you might check this out again if you get your heat scanner fixed.

Anyhow we are getting more and more info which is a good thing and most interesting.

powerade

I am so glad that you are finding this interesting as I am intrigued but also incredibly frustrated. In answer to your question, the boiler did not fire up after the second waiting period. It went straight into rapid anti cycle. Then the boiler fired up and the CH started to demand heat.
When my plumber completed the zoning work he did not install the ABV. When I reported the cycling issue to him back in May of this year he came back out, said that he had forgotten to do something and when I looked in the old hot press I could see that he had installed sonething else as it protruded out beyond the actuators. That transpired to be the ABV. Given that it was an afterthought, I wouldn't be surprised if it was faulty. Thank you for the ABV explanation which I will digest in the morning.

John.G

Saw this somewhere else re anti cycling.

If two on/off cycles take place within the anti cycle set time then the boiler will stay off for the anti cycle set time.

So it will be interesting to see what this set time is.

powerade

I still do not get the role of the ABV in the current configuration of my system as there is one in the boiler, there is the one that was fitted by the plumber and, up until yesterday evening, every radiator was a bypass as all of the TRV heads were removed. The plumber put a few of them back on in Zone 1 last night. He also drained the water out of the radiator in the kitchen. Was that something to do with balancing the system?
Anyway, I have been familiarizing myself a bit more with the manual and I had a look at all of the items on the info menu. Item I2 shows the "appliance previous operational status" which was displayed as d4 Temperature Fault. From page 67 of the manual, the description of this code is "Primary flow temperature rising too fast". There are a number of checks listed which include the pressure, air in the system and circulation within the heating system. I have no idea if this is of any significance but I noticed that the pressure is at 1.5 today wirh the heating off but it is normally at 1.0. Also I checked the Air Purge Mode setting (2.2C) and it is OFF.
Finally, I lowered the max CH output to 16KW (lowest possible setting is 13) and turned on Zone 1. It took 20 minutes to reach flow temperature which is a good bit slower than usual and, consequently, the Zone took longer to heat up. It was only on for one hour and it did not cycle.
I am going to lower the max output again to 13KW, keep an eye on the pressure and I want to measure the return temperature.
Should I change the Air Purge setting and is there a air purge routine that I should run, just in case?

powerade

Just a few more observations. I put a bit if tape on the flow and return pipes ( see photos) and measured the temperature. The flow temp was 29.3 and the return was 30.6. The flow temperature as per the boiler was 58. The bypass pipe is scalding and there appears to be no change in the pressure.

John.G

I'll come back to the ABV role later. I would not change the air purge setting, this may be to do with the boiler furnace air purging before and after firing (and has nothing to do with air in your system) so leave it as is. Re air in your system, just crack open the air vents on the rads and see if you get any air out, a small hiss is no problem, then reclose when water comes out. Once all the air is got rid of its unlikely to return as you have a sealed system. You may have to vent the rads for a bit longer since the kitchen one was drained down.
RE 1.5 bar vs 1.0 bar previously, you should see a flexible hose for topping up purposes adjacent to the pressure gauge, there should be a valve at both ends of these and should be closed, post a pic if not sure. The plumber will have topped up the system after draining down the rad as well so might account for that 1.5 bar.

Table 39
I would check item item 2.3b Anti cycle function (3 to 45 mins) it defaults to 5 min, if it is showing this 5 mins I would suggest reducing it to 3.0

Also item 2.3c Anti cycle temp hysteresis but purely for interest, do not adjust, just note the setting.

The reason for the "Primary flow temperature rising too fast" is probably because with one zone only in service the boiler was firing at full output of 25 kw which you have now reduced to 16kw, it's up to yourself but I would be inclined to let it at 15/16kw in conjunction with reducing the anti cycle time to 3 mins and then try the system on zone2 only and see how it responds.

John.G

I.m afraid that thermal gun you have is pretty useless, just check the temperature on the flow pipe close to where it comes out of the boiler, if its not within 10c of the displayed flow temp, forget it.

powerade

Interesting because the plumber used it last night. I am running Zone 2 right now with the max output down to 12. I was mistaken earlier, you can set it as low as 7. The plumber changed the anti cycle time to 3 minutes last night.
With the max output set at 16kw, Zone 1 temperature increased by 3.1 degrees in 52 minutes and consumed .83 units of gas. With the max output set at 12kw, Zone 1 temperature increased by 1.8 degrees in 52 minutes and consumed .77 units of gas. So, the lower setting made it considerably slower to heat up but consumer almost the same amount of gas. Baffling......

powerade

The anti cycle temperature setting is 6.

John.G

The gas consumption @ the 16 kw setting was 0.83 m3/h and @ the 12 kw setting was 0.77 m3/h... an increase of 7.79%
assuming initial zone temp @ 15C in both cases then after 52 minutes @ 16 kw gave a zone temp of 18.1c & @ 12 kw gave a zone temp of 16.8c.... an increase of 7.7%. You will probably find in practice that the lower power rating will give a very small benefit in fuel economy as it will be running longer with a lower return temp but practically speaking no difference.....what you require is a reasonably quick warm up AND when either zone is satisfied, as consistently a flow temperature as possible while the boiler is cycling. If you find that the 12 Kw gives you the best compromise then fine but you will have to bring the zones in earlier to achieve the set point temp, I would suggest incrementally increasing the max output to ~ 15kw and see how these changes (inc 3 min a.cycle) time deal with zone2.

ABV: Yes, it would seem that there was/is no need to have one in your system as it doesn't mention pump overrun in the manual and the boiler also has its own by pass, possibly to maintain a minimum flow through the boiler when TRV's are closing in. IF a ABV is required/requested by the boiler manufacturer then, in lieu, you cannot use any radiator(s) that are fitted with TRVs or are zone controlled as in both cases they can shut off the circulating flow completely but as I suggested, a rad without a TRV that has its flow piped upstream of any zone valves will provide a permanent path for the circulating water as long as the pump is running even with zone valves and TRVs shut, a towel rad is often utilised for this purpose as you will generally have a wet towel and the weeks washing draped around it and you are not wasting any real energy.
In respect of the ABV fitted in your system, I would suggest, shutting it off completely, even beyond its max setting (clockwise, I think) and then, in the morning as soon as the boiler fires up, keep your hand on the return side of the ABV, this should remain relatively cool even when the flow pipe is roasting, if it seems to be heating up as fast as the flow pipe then its passing/faulty which would be a bit surprising as I reckon that it would have been new. If it is passing, then because you have no idea really how much, get your plumber to renew it even if not required now, you can just leave it shut off and in the event of installing a new boiler sometime down the road which does need a ABV, you have it already in place.

I Am The Law

OP Can I ask you to check the copper pipe shown in Photo1 and state which pipe it's connected to in Photo2?

powerade

It is connected to the return pipe in photo 2.

I Am The Law

Well IMO that's the problem, according to the manual thats the flow from your boiler.

The first problem is it means the bypass valve is the wrong way around and short circuiting the flow and return, causing cycling and so on.

BDI

I’m not reading all that thread, and seems too complicated with all the ideas and heat guns.

Is the room stat in a drafty area or hot to cold area.
If you turn it off does the boiler turn off and does it turn back on when you turn it up again. If you run one zone at a time does only the things that are supposed to work, work?

Is zone two running a heating circuit and hot water cylinder?

Probably faulty wiring job seen as it’s done when the zone valves were added or zone two is leaking so badly into the hot water cylinder that it takes 4 hours to heat it up then when you turn on the tap it needs another 4 hours.

I wouldn’t know without looking at it and have no interest in looking at it or reading the thread to be honest I’m a bit tired but it looks very over complicated.

powerade

I Am The Law wrote: »

Well IMO that's the problem, according to the manual thats the flow from your boiler.

The first problem is it means the bypass valve is the wrong way around and short circuiting the flow and return, causing cycling and so on.

Let me answer your question in a different way. The short horizontal pipe is connected to the flow pipe on the left and the return pipe on the right. The directional arrow on the ABV points from the flow to the return. The plumber was here again this evening and he checked all of the configuration.

John.G

Did he have anything to say about the ABV?. How is your system performing now if in cycling mode?

powerade

BDI wrote: »

I’m not reading all that thread, and seems too complicated with all the ideas and heat guns.

Is the room stat in a drafty area or hot to cold area.
If you turn it off does the boiler turn off and does it turn back on when you turn it up again. If you run one zone at a time does only the things that are supposed to work, work?

Is zone two running a heating circuit and hot water cylinder?

Probably faulty wiring job seen as it’s done when the zone valves were added or zone two is leaking so badly into the hot water cylinder that it takes 4 hours to heat it up then when you turn on the tap it needs another 4 hours.

I wouldn’t know without looking at it and have no interest in looking at it or reading the thread to be honest I’m a bit tired but it looks very over complicated.

It shouldn't be complicated IMO, but I don't have a solution so it clearly is complicated.
I don't have a hot water cylinder and the room stat is located in a draught free. internal corner. The room stat is working as expected and turns the boiler on/off.The problem is mainly with Zone 2, slow to heat and constant anti cycling but it can also happen in Zone 1 if I turn radiators off or lower TzrV settings.

powerade

John, I tested Zone 2 this afternoon with the max KW output set to 16.1. No real change in the rate of temperature increase but the shut downs and rapid anti cycles were almost constant after 25 minutes. My plumber has contacted Worcester Bosch and I am hoping to hear back from him tomorrow. In the meantime, I am continuing to look for information on Google as there are numerous posts from people with similar issues, specifically with Worcester Bosch Greenstar boilers but, as I mentioned before, I have yet to find one with a definitive solution. I'm going to make a You Tube video if we ever crack this

John.G

Very good and is the flow temperature consistent and not falling too low?? remember no matter what solution you come up with.... the boiler will have to cycle on low heat demand, period. Standing back a bit I would insist that either that ABV is renewed or thrown away and a gate valve put in its place because IF it is passing excessively then you are kicking the proverbial up a mountain, I,m amazed your plumber hasn't zoned in on this, its no good going to WB without having the hardware right first.

It's also possible that a bit of crap is trapped in the ABV so he can check for that presuming he can split it open.

Don't bother with google, you will be able to charge them when you tell them how you fixed the problem.

powerade

He only called out because of my persistence. I know that he won't do anything with the ABV no matter how insistent I am and, given that I still don't fully understand how the ABV should be operating, it would be very difficult to present him with a convincing argument to check and/or replace it. If I close it fully and the horizontal.pipe heats up shortly after the heating is turned on, is that definitive proof that it is not working as expected? He will, in all likelihood, say that it's not causing any problems so I really need to understand how the ABV can be causing or contributing to the heating problems. The temperature drops have not been below 55 degrees today, btw.

rightjob!

Its not the by pass valve,are both stats set to max when the boiler shoots up and down in temperature?
Are you sure the zone valves arent closed when this is happening?
Its that or else sludge in the system

John.G

powerade wrote: »

He only called out because of my persistence. I know that he won't do anything with the ABV no matter how insistent I am and, given that I still don't fully understand how the ABV should be operating, it would be very difficult to present him with a convincing argument to check and/or replace it. If I close it fully and the horizontal.pipe heats up shortly after the heating is turned on, is that definitive proof that it is not working as expected? He will, in all likelihood, say that it's not causing any problems so I really need to understand how the ABV can be causing or contributing to the heating problems. The temperature drops have not been below 55 degrees today, btw.

You don't need to know how a ABV works, all you need to know, despite some rather one or two daft comment(s) stating "its not the bypass" is that when you WANT no bypass that you will get it, otherwise, you may as well just stick that piece of pipe to just "short circuit" the flow & return OR install a gate valve to give no by pass or whatever.

John.G

John.G wrote: »

You don't need to know how a ABV works, all you need to know, despite some rather one or two daft comment(s) stating "its not the bypass" is that when you WANT no bypass that you will get it, otherwise, you may as well just stick that piece of pipe to just "short circuit" the flow & return OR install a gate valve to give no by pass or whatever.

John how many gas boilers have you commissioned or repaired? I ask because your giving advice on the characteristics of a gas boiler and deciding other posters views are daft.

You have posted some comments that I don’t agree with as they don’t match my own findings but I’m not attacking your views.



Also please don’t call posters daft or I’ll have to put my moderator hat on.

K.Flyer

powerade wrote: »

I still don't fully understand how the ABV should be operating.

In simple terms it is a spring loaded valve in which you can adjust the load on the spring.
You set the load on the spring so that the valve remains closed during normal heating / hot water circuit operation and should only open when there is back pressure from all the zone valves having closed or all the trv valves having closed, in other words, when there is nowhere else for the water being pumped around circuits to go.
If on a particular circuit it cannot be adjusted to stay closed during normal operation and radiators are not heating correctly, then the radiator lock shield valves on that circuit need to be checked to ensure that they are opened sufficiently and the system is balanced.
If the bypass remains open with little to no back pressure from the circuit, then the by pass may be faulty or is being held open from debris in the heating system.

John.G

gary71 wrote: »

John how many gas boilers have you commissioned or repaired? I ask because your giving advice on the characteristics of a gas boiler and deciding other posters views are daft.

You have posted some comments that I don’t agree with as they don’t match my own findings but I’m not attacking your views.



Also please don’t call posters daft or I’ll have to put my moderator hat on.

Gary,

It certainly wasn't my intent to call anyone daft and apoligies if I gave that impression, I thought the comment( s) was "daft" but ONLY in the context that the OP has repeatedly stated that the ABV is faulty. Personally, I wouldn't take the slightest umbrage if someone called one of my statements daft, I would certainly either agree or defend it robustly.

Re boiler experience: I had over 40 years experience in the running and maintenance of oil fired boilers. I was involved in the conversion of a number of 50 MW oil fired boilers to enable them to burn either oil only or natural gas only or Natural gas + Biogas and the subsequent maintenance of these boilers including all the control/safety devices involved in the burner control/management.

May I ask why do you agree that the by pass isn't a problem?.

John.G

powerade wrote: »

He only called out because of my persistence. I know that he won't do anything with the ABV no matter how insistent I am and, given that I still don't fully understand how the ABV should be operating, it would be very difficult to present him with a convincing argument to check and/or replace it. If I close it fully and the horizontal.pipe heats up shortly after the heating is turned on, is that definitive proof that it is not working as expected? He will, in all likelihood, say that it's not causing any problems so I really need to understand how the ABV can be causing or contributing to the heating problems. The temperature drops have not been below 55 degrees today, btw.

The proof is that the boiler circulating pump is configured to give a constant head (pressure) of 3M and if you have the ABV setting at anything higher than 0.35 which is 0.35 bar or 3.5M then the ABV is shut and should not pass any water through it.
If your plumber doesn't accept this and you are quite sure that it is passing even when fully shut (index 0.5 or higher) then get another plumber to change it or fit a gate valve, period, otherwise IMO you will never be able to fine tune your system.

John.G

John.G wrote: »

Gary,

It certainly wasn't my intent to call anyone daft and apoligies if I gave that impression, I thought the comment( s) was "daft" but ONLY in the context that the OP has repeatedly stated that the ABV is faulty. Personally, I wouldn't take the slightest umbrage if someone called one of my statements daft, I would certainly either agree or defend it robustly.

Re boiler experience: I had over 40 years experience in the running and maintenance of oil fired boilers. I was involved in the conversion of a number of 50 MW oil fired boilers to enable them to burn either oil only or natural gas only or Natural gas + Biogas and the subsequent maintenance of these boilers including all the control/safety devices involved in the burner control/management.

May I ask why do you agree that the by pass isn't a problem?.

Truth be told this post has become far to complex for me so I’m staying out of it I have a far more simple approach but to answer your question it’s not unusual to see gas boiler act in this way and I would be surprised if it was the bypass but everyday is a learning day.

Wearb

K.Flyer wrote: »

In simple terms it is a spring loaded valve in which you can adjust the load on the spring.
You set the load on the spring so that the valve remains closed during normal heating / hot water circuit operation and should only open when there is back pressure from all the zone valves having closed or all the trv valves having closed, in other words, when there is nowhere else for the water being pumped around circuits to go.
If on a particular circuit it cannot be adjusted to stay closed during normal operation and radiators are not heating correctly, then the radiator lock shield valves on that circuit need to be checked to ensure that they are opened sufficiently and the system is balanced.
If the bypass remains open with little to no back pressure from the circuit, then the by pass may be faulty or is being held open from debris in the heating system.

Are some of them also installed to give a minimum return temperature to the boiler to prevent thermal shock?

powerade

WRT the ABV, I closed the valve fully,I.e. just lpast the 0.5 setting and turned on Zone 1at 9.28am. All of the pipes were cold at this point. The flow temperature started at 32 degrees and rose to 59 degrees by 9.35. At this point the flow pipe was very warm, the horizontal bypass pipe was also very warm (not quite as warm as the flow) and the return pipe was cold.By 9:37 the return pipe was getting warm and the flow temperature was up to 66. Since then the flow temperature moved between 66 and 65 degrees but it has not cycled. At 10:12 the horizontal and return pipes are scalding and the return pipe is marginally cooler. The room stat has risen from 13.6 to 16.6, set point is 18.
The max output is set at 24kw. My very simplistic understanding of the operation of the system is as follows:
Heating starts up and belts out water that should eventually reach the set flow temperature of 65 degrees. The water flows into each of the radiators (not sure if this happens sequentially), the radiators start to warm up and dissipate heat. At some point the water returns to the boiler and the boiler measures the return temperature. If the return temperature is higher than the boiler is expecting (not sure how that is calculated), the boiler output is 》the combined radiator output and the boiler will modulate down, subject to a lower limit of 7kw. If 7kw is still not low enough the bypass should kick in. That is what logically makes sense to me. If it is that simplistic and everything is working as expected then the boiler, in theory, should never cycle. Am I on the right track here?
In Zone 1, if all 5 radiators are fully on, the output is around 9.5kw. The boiler should be able to modulate down to that level of output without needing the bypass. If I turn off a couple of radiators, however, and reduce the output to 《7kw, Zone 1 will behave exactly the same as Zone 2.
Given that the horizontal pipe heats up almost at the same time as the flow pipe, with the ABV closed, is that just latent heat or actual water?
Just to continue with my simple logic, given that the radiator KW output in Zone 2 will always be 《7kw, should a correctly working bypass manage the deficit between the boiler and radiator output and prevent anti cycling?
In Zone 2 the flow temperature climbs up to 69 degrees and then the system shut down & anti cycling starts. Is that temperature rising because the system cannot balance the boiler and radiator output, for whatever reason ?
I am sorry for all of these questions but, if I have a basic understanding of the logic if what should be happening, it is a lot easier to interpret what is actually happening.

powerade

rightjob! wrote: »

Its not the by pass valve,are both stats set to max when the boiler shoots up and down in temperature?
Are you sure the zone valves arent closed when this is happening?
Its that or else sludge in the system

The boiler only shoots up and down when Zone 2 is on (or less than 5 radiators in Zone 1). The manual dial stat is set to max, the digital room stat is typically set between 21 and 22 degrees. The actuator light on the Zone 2 valve and the red demand lights on the boiler remain illuminated when the temperature starts to rise.

John.G

The by pass is only there to dissipate heat from the boiler when it shuts down and also in some cases, as wearb pointed out, to maintain a minimum flow through the boiler as TRvs shut in but in your case the boiler has a internal by pass which should maintain this minimum flow. As no mention of pump overrun is mentioned then presumably this boiler does not need to dissipate the heat. With the external by pass the heat is simply dissipated in the pipework due to radiation and is very little so even though your thinking is logical it really wouldn,t help in any significant way to help reduce the boiler cycling at reduced load and might actually make it worse as you could be introducing very hot water to the return which, when mixed with the far cooler return water from the rads will result in a far higher temperature than desirable and this is why it is so important that the ABV is tight. There is no return temperature sensor on this boiler, it modulates down when the flow temperature approaches the set point and if/when it exceeds this setpoint by ~ 5C, it shuts down. It is quite normal for a boiler to cycle when the heat requirement is < the minimum boiler output but WB do seem to have a "probem" with this. Its a bit ironical but there are still gas boilers running that have no modulation and seem to work away OK.

You now have the boiler at 25KW output? so when its recycling what is the lowest flow temperature? if its not more than 10 to 12 deg lower than the setpoint then you should be reasonably happy, oil fired boilers spend their whole lifetime operating in cycling mode and the flow temperature will rise/fall by this margin during each cycle. Obviously, it would be nice if gas boilers didn't cycle and some like Vokera can modulate down to ~ 2 kw.

K.Flyer

The bypass valve does not react to temperature or heat outputs, it reacts to back pressure and flow rates.
If the connecting pipe from the bypass to the return is "scalding hot" and your #2 zone is still open and stat calling for heat, and heating space not satisfied, then you have a circulation issue.
Things to check;
1- Fault with bypass valve.
2- Fault with zone valve not opening fully.
3- Incorrectly set lock shield valves.
4- TRVs set too low.
5- Obstruction in pipework circuit.

powerade

John, thank you so much for your patience, it is much appreciated. I have a few final questions and then I am going to leave it to my plumber and Worcester Bosch. Hopefully my next post will be the solution
1. Should my boiler modulate?
2. When demand is 《7KW, is that what drives the flow temperature up?
3. How does the boiler know that it needs to modulate up or down if the return temperature is not measured
4. When the system shuts down the bypass kicks in to dissipate the extra heat, right? Given that I have seen multiple shut downs precede a rapid anti cycle, is it the case that the system will keep shutting down until the temperature has reached the desired level ?
5. What is the point of the rapid anti cycle if the shut downs and by pass are lowering the temperature.
That's it for now and thanks again.

John.G

1. Yes, and it does, if you mean should it cycle, then yes, it should and does, sort of.

2. The heat input to the boiler is greater than the heat being emitted by the rads, this excess heat has to go somewhere so it continues to heat up the water.

3.Because it only uses the flow temperature as the measurement, at full firing the heat input is far greater than the rad output so the water continues to heat up and as the temperature approaches its set point then the boiler gas flow is reduced (modulating) until the setpoint temperature and the (flow) temperatures are the same. It will stay at this steady firing rate until say one zone is shut off, the temperature will again start to rise and the firing rate will reduce until the flow temperature matches the set point, and vica versa, if another zone is opened the flow temperature will reduce and the boiler will increase its firing rate until the flow temperature and the set point are again equal.
All boilers use this as the main controlling sensor but some also use the return temperature as a controlling influence as well.

4, The system will only shut down if all zone valves shut. if the flow temperature rises ~ 5C above its setpoint then the burner only will stop firing, the circulation pump will continue to run until the flow temperature again reaches its set point, at which time the boiler burner will refire and if its minimum output is higher than the rads output it will again shut down when the temperature is 5C above its setpoint, the anti rapid cycle time (in theory anyhow) should just give a 3 minute delay before the next cycle commences but again in theory this should only happen if there are two consecutive (on/off) cycles within this 3 minute period.

5. That is the $60,000 question. As I said previously if the drop in temperature is 10 to 12C consistently, then I would be quite happy with this but apparently its not doing this now?? and when you lowered the max output to 12 kw, was it ok and was it OK at 16kw. ALL the posts that I have also read re WB boilers would suggest that this is at least a partial solution to the problem. Also don't get fobbed off by WB saying that the boiler should not cycle, I will repeat what I've said before, my relations 20 kw Vokera often servicing one zone with only 3 rads cycles on/off without a bother, when I next visit I will check to see how low the flow temperature gets during this cycling.

Note: The by pass doesn,t or shouldn't operate during this cycling period at all, its only if the whole system shuts down that the by pass comes into play really, with your boiler the only by pass in play is its internal one and this does nothing when the whole system shuts down as apparently there is no pump overrun.

powerade

Thank you again John. I just want to ensure that I am using the correct terminology. When I use the term modulate I mean is the boiler adjusting its KW output because the flow temperature is greater than the set point. Given that there is a maximum and minimum output KW setting, I assumed that was the case. ls that what is happening when the boiler gas flow is reduced?
If the temperature rises to 5 degrees or more above the set point, is that because the system cannot modulate any more, i.e. it is down to the lowest KW output and that's still greater than the radiator demand? That's when the burner stops firing (status 204) and that is what I have been referring to as a system shutdown. Typically there will be two followed by a rapid anti cycle. The system is basically paused to try to reduce the flow temperature, right ?
When I lowered the maximum KW output to 16.1 and 12 when I was just running Zone 2, the boiler constantly had a 204 status and there were sometimes 3 or 4 204's before the anti rapid cycle. The rate of temperature increase, however, appeared to be unaffected. I really wasn't expecting that result .....Given that one of the functions of the bypass is to dissipate heat, it sounds like this was working less effectively when I lowered the KW output. I am sure that there is no connection but I'm just putting it out there. Just to be absolutely sure that I have understood some of your previous comments about the by pass function, am I correct in saying that the by pass should dissipate heat when the boiler status is 204.?

powerade

K.Flyer wrote: »

The bypass valve does not react to temperature or heat outputs, it reacts to back pressure and flow rates.
If the connecting pipe from the bypass to the return is "scalding hot" and your #2 zone is still open and stat calling for heat, and heating space not satisfied, then you have a circulation issue.
Things to check;
1- Fault with bypass valve.
2- Fault with zone valve not opening fully.
3- Incorrectly set lock shield valves.
4- TRVs set too low.
5- Obstruction in pipework circuit.

Thank you. All of the TRV's have been removed so we can rule no 4 out. How can I tell if the lockshields are incorrectly set? Is that a balancing issue?

John.G

Yes, you are correct re modulation.... then "If the temperature rises to 5 degrees or more above the set point, is that because the system cannot modulate any more, i.e. it is down to the lowest KW output and that's still greater than the radiator demand? That's when the burner stops firing (status 204)"

Status 204 is system waiting, primary flow temperature greater than set point temperature. The burner shuts down but the circ pump keeps running until the primary flow temperature reaches the set point temperature, this is NOT system shutdown, the burner should then come back on fairly rapidly because the rads are cooling the water down

"and that is what I have been referring to as a system shutdown. Typically there will be two followed by a rapid anti cycle. The system is basically paused to try to reduce the flow temperature, right ?"
I presume you are saying that there are 2 two system waitings followed by a rapid anti cycle? the system waiting should really cool the system down (via the rads). Here is my complete answer again from one of the posts.

4, The system will only shut down if all zone valves shut. if the flow temperature rises ~ 5C above its setpoint then the burner only will stop firing, the circulation pump will continue to run until the flow temperature again reaches its set point, at which time the boiler burner will refire and if its minimum output is higher than the rads output it will again shut down when the temperature is 5C above its setpoint, the anti rapid cycle time (in theory anyhow) should just give a 3 minute delay before the next cycle commences but again in theory this should only happen if there are two consecutive (on/off) cycles within this 3 minute period.

"The rate of temperature increase, however, appeared to be unaffected. I really wasn't expecting that result .....Given that one of the functions of the bypass is to dissipate heat, it sounds like this was working less effectively when I lowered the KW output."

What do you mean by the rate of temperature increase, however seems to be unaffected.? The function of the by pass (as I stated previously) should only operate when the whole system shuts down IE all zone valves shut but no effect with this boiler since no pump overrun.

Now can you please do the following tests on zone 2 only and calling for heat in all 3 cases.

1. Set max output to 25kw and just tell me what is the lowest flow temperature during the cycling/anticycling. (Don't need any other information)

2. Set max output to 16kw and just tell me what is the lowest flow temperature during the cycling/anticycling. (Don't need any other information)

3. Set max output to 12kw and just tell me what is the lowest flow temperature during the cycling/anticycling. (Don't need any other information)

powerade

There were two reasons why I started this thread as follows;
1. The temperature is Zone 2 is very slow to increase and it can take hours to get it to the set temperature
2. The boiler, after a short period of time, will pause (system waiting) and cycle resulting in the radiators cooling off if I am running Zone 2 on its own. . This, in all likelihood, is contributing to issue no 1.

The rate of temperature increase that I referred to in my previous post is the rate of Zone 2 temperature increase.

I will let you know the results of the tests that you have advised me to carry out.

K.Flyer

K.Flyer wrote: »

The bypass valve does not react to temperature or heat outputs, it reacts to back pressure and flow rates.
If the connecting pipe from the bypass to the return is "scalding hot" and your #2 zone is still open and stat calling for heat, and heating space not satisfied, then you have a circulation issue.
Things to check;
1- Fault with bypass valve.
2- Fault with zone valve not opening fully.
3- Incorrectly set lock shield valves.
4- TRVs set too low.
5- Obstruction in pipework circuit.

powerade wrote: »

Thank you. All of the TRV's have been removed so we can rule no 4 out. How can I tell if the lockshields are incorrectly set? Is that a balancing issue?

Yes they are used for balancing the system.
You could start by rotating each one a full turn anti-clockwise to increase the flow through the radiators.
A simple exercise, but just to see if that changes anything.

powerade

John, before I test Zone 2 again, can you let me know if you want me to leave the ABV closed?

John.G

Yes, thanks.

powerade

Okay. Just to advise of a new scenario that I have not seen before but it may or may not be relevant. I have just been running Zone 1 this morning with a stat temperature of 18 degrees. I heard the boiler come on as the Zone 2 start time kicked I. I immediately turned Zone 2 off and a few seconds after I saw the blue demand light for Zone 1 come on. I checked the boiler status and it was 202. I then checked the flow temperature and it was 29 degrees. By the time I got my phone it was down to 27 and it settled at 25 (photos attached). The boiler fired and the temperature started to climb. It was not running at 24KW, to the best of my knowledge, judging by the noise of the boiler but by the time that the flow temperature had reached 44 degrees it was pretty noisy again. I'm not looking for feedback, I just wanted to mention it as it might throw up some new clues.

I Am The Law

powerade wrote: »

Let me answer your question in a different way. The short horizontal pipe is connected to the flow pipe on the left and the return pipe on the right. The directional arrow on the ABV points from the flow to the return. The plumber was here again this evening and he checked all of the configuration.

Is this how your system is piped OP?

powerade

K.Flyer wrote: »

The bypass valve does not react to temperature or heat outputs, it reacts to back pressure and flow rates.
If the connecting pipe from the bypass to the return is "scalding hot" and your #2 zone is still open and stat calling for heat, and heating space not satisfied, then you have a circulation issue.
Things to check;
1- Fault with bypass valve.
2- Fault with zone valve not opening fully.
3- Incorrectly set lock shield valves.
4- TRVs set too low.
5- Obstruction in pipework circuit.

Can I just ask a quick question regarding the lockshield valves. When the heating was split into two zones, the plumber replaced all of the TRV's and the lockshield valves. I tried to turn a couple of then in Zone 2 and they were extremely difficult to turn in either direction. I did manage to open two of them by approx one turn and, almost immediately, I could feel a difference in the radiator temperature. Is there any harm in opening them any further?

John.G

Was on another mission to relation's house and she kindly let me take a few readings off the above boiler which has a max output of 20 kw with a minimum output ~ 5.4 kw and a anti cycle time of 3 minutes.
One zone has 3 rads on it so I carried out the test with 2 rads of combined output of ~ 3.5 kw.
This boiler has a total hysteresis of 10C...cut in = SP-5C & cut out = SP+5c.
I set it to 70C so cut in = 65C & cut out = 75C.
From cold (two rads, 3.5kw). The temperature climbed to 71C in ~ 8 minutes and then over the next 5 or 6 minutes climbed to its cut out (burner off) temperature of 75C. The temperature then fell to 61C in ~ 3 to4 min, the burner then refired and in 30 secs or so climbed to 72C and then again over the next ~ 4 mins it reached its cut out temp of 75C. It did this consistently while I watched 4 cycles.
So the average flow temperature over these periods was a excellent 68C.

The temperature difference between the Flow & return was 10C/13C.

John.G

powerade wrote: »

Can I just ask a quick question regarding the lockshield valves. When the heating was split into two zones, the plumber replaced all of the TRV's and the lockshield valves. I tried to turn a couple of then in Zone 2 and they were extremely difficult to turn in either direction. I did manage to open two of them by approx one turn and, almost immediately, I could feel a difference in the radiator temperature. Is there any harm in opening them any further?

I must confess I thought that they were all fully open, maybe your plumber throttled them in a few days ago, to adjust/open/close you sometimes have to remove the plastic cover and use a adjustable spanner, it should be ~ 3 full turns from closed to open, I would suggest closing them fully, then reopen fully ~ 3 turns and leave them like this + all TRVs fully open (Zone2, the cold one) you will then also be able,IMO, to carry out more meaningful cycling tests.

powerade

Thank you, I will do that.