Plumbers advice PLEASE!

caspermccormack

Hello,

I'm looking for some answers to the following questions but first i'll explain what it is i'm doing.

On Saturday I'm installing a 20" grant triple pass back boiler back into my fire place. I have a new chimney breast built 6 years ago with a flu liner installed. First I'm knocking back the breast and fitting back the clay liners and flu gather. I'm currently using a gas central heating system for hot water and heating the house.

The gas boiler i have is a potterton prima, and is a open vented system(has it's own header tank in the attic) which works fine.

What I want to do is have the back boiler work in line with the gas boiler so if the solid fuel is not hot enough to heat the house that the thermostat in the gas boiler will allow its self to switch on and keep the heating topped up. Is this possible to do? Would it work using the same pump on the gas boiler to circulate the hot water from the back boiler?

And if the fire was not lighting, i would like for some type of fitting to not allow flow through from the gas boiler to heat the back boiler(waste of heat straight up the chimney).

Is there a way of doing this through automated valves?

Any advice would be great, or if some body has had this work done before let me know and i'll contact them for some advice.

Kind regards
Anthony

ART6

One way would be to fit a thermostat to the riser pipe (the top one) from the back boiler and have that operate a solenoid valve just downstream of it in the same pipe. Then when the back boiler is generating heat the valve would open once a set temperature had been reached. You could check out www.intercontrols.com for suitable valves. Plumbers suppliers should have suitable clamp-on thermostats.

The things you would need to allow for though are that the back boiler is in the flow circuit from the gas boiler, and that the gas boiler circulating pump is started by a thermostat that is independant of the gas boiler, otherwise if the gas boiler was turned off then the back boiler would get no circulation and would overheat.

caspermccormack

Thanks for the reply, the pump on the gas heating system works if the gas boiler is switched on and the heat setting turned down to zero, so would this be ok?. If the heating was say set at setting number3 the gas would come on until the thermostat in the gas boiler got to the temp to switch it off, so if the fire was lit and the back boiler was generating heat would it keep the gas boiler switched off through the thermostat? So if the fire was lit at night supplying all the heat until the early hours after it died down the gas would come back on to keep up the heating?

The fittings for the back boiler i'm a little confused about. The flow and return heating pipes run up along the chimney breast, so you say i need to tap into the flow pipe. I assume you mean flow from the gas to the bottom of the back boiler and the top out to the other side of the flow pipe. Is this where i should install the thermostat switch and then some kind of shut off valve? Would that stop the heating flowing upstairs? or would the flow coming from the gas boiler(hot water) not open the valve? Hope this is clear? again any info would be great.

Anthony

caspermccormack

ART6 wrote: »

One way would be to fit a thermostat to the riser pipe (the top one) from the back boiler and have that operate a solenoid valve just downstream of it in the same pipe. Then when the back boiler is generating heat the valve would open once a set temperature had been reached. You could check out www.intercontrols.com for suitable valves. Plumbers suppliers should have suitable clamp-on thermostats.

The things you would need to allow for though are that the back boiler is in the flow circuit from the gas boiler, and that the gas boiler circulating pump is started by a thermostat that is independant of the gas boiler, otherwise if the gas boiler was turned off then the back boiler would get no circulation and would overheat.

Had a look at the link to intercontrols.com not to sure its the right site, they do all types of camera equipment.

ART6

caspermccormack wrote: »

Thanks for the reply, the pump on the gas heating system works if the gas boiler is switched on and the heat setting turned down to zero, so would this be ok?. If the heating was say set at setting number3 the gas would come on until the thermostat in the gas boiler got to the temp to switch it off, so if the fire was lit and the back boiler was generating heat would it keep the gas boiler switched off through the thermostat? So if the fire was lit at night supplying all the heat until the early hours after it died down the gas would come back on to keep up the heating?

The fittings for the back boiler i'm a little confused about. The flow and return heating pipes run up along the chimney breast, so you say i need to tap into the flow pipe. I assume you mean flow from the gas to the bottom of the back boiler and the top out to the other side of the flow pipe. Is this where i should install the thermostat switch and then some kind of shut off valve? Would that stop the heating flowing upstairs? or would the flow coming from the gas boiler(hot water) not open the valve? Hope this is clear? again any info would be great.

Anthony

caspermccormack wrote: »

Had a look at the link to intercontrols.com not to sure its the right site, they do all types of camera equipment.

If the circulating pump runs with the gas boiler setting down to zero then you should be OK with circulating the back boiler, but you will need to make sure that the back boiler circuit is in parallel with the gas boiler circuit -- in other words that the back boiler pipes tap into the main flow pipe in the same way that radiators do. That means that the gas boiler can push water past the back boiler rather than through it. Then when the fire is not lit and you have a solenoid valve and a thermostat in the back boiler circuit, there will be no flow through the back boiler. Where you put the valve doesn't matter as long as it is in one of the back boiler pipes, but the thermostat must be in the flow. That will be the pipe coming from the top of the boiler, and will be the one that gets hot when the fire is lit. With the valve closed there will be no flow through the back boiler and therefore nothing to trigger the thermostat.

The web site I gave you was subject to my finger trouble. It should have been http://www.intelcontrols.com :rolleyes:

JamesM

It's not as simple as you think. I think that you will find that to be legal and safe, you must have a circuit from the back boiler up to a seperate (extra) coil in the hot water cylinder, and then on up to a header tank in the attic. After that, you can just link into the existing gas system.
Jim.

caspermccormack

JamesM wrote: »

It's not as simple as you think. I think that you will find that to be legal and safe, you must have a circuit from the back boiler up to a seperate (extra) coil in the hot water cylinder, and then on up to a header tank in the attic. After that, you can just link into the existing gas system.
Jim.

thanks for the advice Jim, I've heard this before alright and was then informed that it only applys to condensing pressurized systems?

caspermccormack

ART6 wrote: »

If the circulating pump runs with the gas boiler setting down to zero then you should be OK with circulating the back boiler, but you will need to make sure that the back boiler circuit is in parallel with the gas boiler circuit -- in other words that the back boiler pipes tap into the main flow pipe in the same way that radiators do. That means that the gas boiler can push water past the back boiler rather than through it. Then when the fire is not lit and you have a solenoid valve and a thermostat in the back boiler circuit, there will be no flow through the back boiler. Where you put the valve doesn't matter as long as it is in one of the back boiler pipes, but the thermostat must be in the flow. That will be the pipe coming from the top of the boiler, and will be the one that gets hot when the fire is lit. With the valve closed there will be no flow through the back boiler and therefore nothing to trigger the thermostat.

The web site I gave you was subject to my finger trouble. It should have been http://www.intelcontrols.com :rolleyes:

That what i was thinking, so the back boiler should connect to the flow and return pipes of the house central heating?

JamesM

caspermccormack wrote: »

thanks for the advice Jim, I've heard this before alright and was then informed that it only applys to condensing pressurized systems?

Condensing systems were not around when this became the rule. See the diagram on this page http://www.solidfuel.co.uk/frame/main.html (You have to click on "Heating Appliances" and then on "Link Up") You must hve a seperate coil in the cylinder and a feed continuing on up to a header tank in the attic. If you do not do this, I believe you would not be insured if there was an accident.
Jim.
Also see this page from Firebird http://www.firebird.ie/installation/BackboilerA3.pdf

caspermccormack

Here is what it looks like in theory, Let me know where the valves or any other bits need to go to make this work.

Thanks for the info.

Regards, Anthony

caspermccormack

If some one can throw some more light on to this as i hope to start work saturday!

JamesM

caspermccormack wrote: »

Here is what it looks like in theory, Let me know where the valves or any other bits need to go to make this work.

Thanks for the info.
Regards, Anthony

I'm not a plumber, but I'm sure that it won't work. You must have the hot flow coming out the top of the back boiler and branching in to the top of the coil in the cylinder, then on up over the header tank. You must also have a cold feed from the bottom of the header tank down, branching into the cylinder, and on down to the back boiler. Once you have those, then you can link into the main heating system.


In your drawing, the cold flow back to the gas boiler from the cylinder and upstairs rads is pushing against the hot water which has risen to the top of the back boiler and is trying to rise up to the cyl and upstairs rads.

I supose that the main safety issue is that you don't have a cold feed, if the back boiler should overheat.

Here is a system I have just found - using something called a "Neutralizer" It should work. http://www.solidfuel.co.uk/pdfs/link_up.pdf
Jim.

caspermccormack

Fair play to you Jim, sure your really looking into this, many thanks. The problem i have to install pipes up to the cyclinder would involve me lifting up floors and breaking plaster all upstairs, the hot press is on a different side of the house from the chimney breast. As with the lay out i have drawn up its rough enough and needs some more detail work with motorized valves, powered by thermostats.

It will probably never be used with the gas on anyway which would give it the access it needs to the vent in the attic if it overheats. I would of thought that its connected up like another rad only its a heat source but still being pumped around buy the original pump. I don't see a reason why it wouldn't work, or why a separate coil is needed in the cyclinder ?

Still confuessed,
Anthony

ART6

It is difficult to know what to advise, since I don't know the layout of your house, and i am not clear about your drawing, but I think JamesM has a point. If your house is a normal 2-storey with the gas boiler in the kitchen, then how best to connect in the back boiler and how to vent it depends a lot on where it is in relation to the gas unit. Going by your drawing, and assuming that the flow from the gas boiler is the red colour, with the circulating pump in that line, then the way you have shown the back boiler would cause it to short circuit the system -- in other words when the fire thermostat operated, hot water would flow from the top of the boiler into the return line to the gas boiler rather than going to the radiators. The downstairs rads might work, but the upstairs ones almost certainly wouldn't unless they could claim some flow by natural thermal circulation (heat rises). Also, you have shown the hot water cyclinder being fed from the radiator line from the circulating pump, when more commonly the cylinder is fed by natural circulation from the gas boiler simply because it is above it. In other words it is in parallel with the rad circuit but not part of it. That way the gas boiler can keep the cylinder hot when the central heating is off and the pump isn't running.

If your circuit is as you have shown, then I think you will need to use two solenoid valves. You would need to tap off the inlet to the back boiler (the bottom connection) from the pumped flow line, and then tap the flow from the back boiler (the top one) back into the pumped flow line. Then, between the two connections, you would need to put a valve that would close when the back boiler heats up, so that all pumped flow is then through the back boiler. The second solenoid valve should then be in the feed pipe to the bottom of the back boiler, and should open when the thermostat detects heat from the back boiler. The thermostat should be in the flow from the back boiler but well back from the connection to the main flow pipe.

Both solenoid valves would need to be switched by the same thermostat. That way you would avoid circulating hot water from the gas boiler through the back boiler and triggering the thermostat when the fire isn't lit. It would also ensure that if the fire was lit but the inlet valve didn't open for any reason, the back boiler could still vent into the main flow line.

In addition, if your existing circuit is anything like you have shown, then it might be that the existing vent pipe to the roof tank would be enough to vent the back boiler, but you would need to check that to make sure.

On the subject of a cold feed to the back boiler, I was assuming that your gas unit is in your kitchen, as I said above, so it's cold feed might be enough to serve the back boiler.

One last point -- your drawing doesn't show any vent directly from the gas boiler. Are you sure that's the case?

caspermccormack

The gas boiler is in the kitchen about 30 foot away from the fireplace. The gas boiler has a cold feed at the bottom, flow and return at the top with each having its own fitting on top to release air i think, and i can drain the system from there. The hot press is upstairs and no way near on top of the boiler to keep water hot. The cyclinder is connected to the same circuit as the rads therefor if the gas is not on I use the immersion for hot water. The two motorized valves that i need will work in reverse of each other? Do they need to be ordered that way or are they switchable from the box( open with thermostat or close).

Thanks
Anthony

ART6

Try taking a look at http://www.seitron.it/fileindexed/product/item/file0003281.pdf That shows a three way valve that is available from Intelcontrols. Using one of those, if you look at Fig. 3 on the pdf sheet and think of the main flow pipe from the gas boiler split and conncect into ports 3 and 2 (port 3 inlet, port 2 outlet) then take a pipe from port 1 to the inlet of the back boiler, and then take the outlet from the gas boiler and tee it into the main flow pipe downstream of the connection from port 2 on the valve.

With that set up you would only need one valve, and that would divert the flow through the back boiler when its thermostat detected heat. In its power off state the valve would be open to full flow through the main flow pipe so would be fail safe as far as the gas boiler is concerned.

The only concern then would be that in the event that the valve failed to open when the fire was lit, then with no separate cold supply to the back boiler it could overheat and generate steam.

Even a 15 mm supply to the back boiler would overcome that if you can find a way of fitting one in.

JamesM

My main point is the safety side of things - I remember so many stories back in the 80s when everyone was getting in back boilers. Any one who just connected in a back boiler to a system with 2 pipes was a cowboy and was hugely endangering the people who lived in the house. I saw many of these systems back then.

There is no thermostatic control on a back boiler - it can overheat - the water can boil and the back boiler can run dry and burst. This will shower the room and people in it with hot coals and boiling water - This has happened :eek:

To avoid this happening, there must be a "heat sink" (hot water cyinder) to take the extra heat that can build up. Also there must be a vent up to the expansion tank, and a cold feed down from the expansion tank, so if the water boils off, cold water will take its place in the back boiler. There must be no valves of any kind in this circuit - nothing that can be turned off, or messed with by the householder.
I'm not sure where you find this in rules or building regulations or whatever, but it is the law, and insurance companies will not cover you if the system is not installed correctly, and there is an accident.
I'm not trying to complicate things, just trying to help
Jim.

John mac

JamesM wrote: »

There is no thermostatic control on a back boiler - it can overheat - the water can boil and the back boiler can run dry and burst. This will shower the room and people in it with hot coals and boiling water - This has happened :eek:

To avoid this happening, there must be a "heat sink" (hot water cyinder) to take the extra heat that can build up. Also there must be a vent up to the expansion tank, and a cold feed down from the expansion tank, so if the water boils off, cold water will take its place in the back boiler. There must be no valves of any kind in this circuit - nothing that can be turned off, or messed with by the householder.
I'm not sure where you find this in rules or building regulations or whatever, but it is the law, and insurance companies will not cover you if the system is not installed correctly, and there is an accident.
I'm not trying to complicate things, just trying to help
Jim.

they should have a Pressure relief valve fitted. (gas boilers and oil have them built in to internal pipework)

JamesM

John mac wrote: »

they should have a Pressure relief valve fitted. (gas boilers and oil have them built in to internal pipework)

A safety valve should be fitted close to the back boiler, in case the pipes in the attic freeze and a fire is then lit, but it is not enough - the heat of the fire can split the metal and the boiler can still burst :eek:
Jim.

caspermccormack

Ok, heres some more info,

I have opened up a valve on a rad and let the water run out without the gas boiler on and the header tank in the attic started to fill. So does this mean that the back boiler will be getting a cold feed through the same way.

With the motorized valve open with a fire lit will give the back boiler access to the header tank if things got to hot.

I don't think I will be running both systems together anyhow, however the point of this going in is to reduce the gas bill, which is only getting more expensive.

JamesM

caspermccormack wrote: »

Ok, heres some more info,

I have opened up a valve on a rad and let the water run out without the gas boiler on and the header tank in the attic started to fill. So does this mean that the back boiler will be getting a cold feed through the same way.

With the motorized valve open with a fire lit will give the back boiler access to the header tank if things got to hot.

I don't think I will be running both systems together anyhow, however the point of this going in is to reduce the gas bill, which is only getting more expensive.

I hate to keep saying it BUT - if the power goes and the fire is going full belt, then the motorised valve will close and the water boils and no cold feed gets through to the back boiler - BOOM.
I always remember the story: Granny is babysitting the kids in the middle of winter. The electricity goes off - no central heating. Granny gets the great idea of lighting the fire and gathers the kids around it. BUT, the water pump is not circulating and maybe also the solenoid valve is off. The water boils and BOOM :eek: This only happened because there was not an open circuit right up through the hot water cylinder on up to the header tank.
This is the reason that it is illegal.
Jim.

caspermccormack

I see your point Jim,

If the fire had the open valve with the power off then this would be ok? Then if the Gas boiler is on the thermostat on that should then switch the valve over to the gas boiler, in the event of a power cut the gas would go out anyway. Makes great reading this.:)

Anything you do must agree with the gas boiler and back boiler manufactures instructions, because if anything went pear shaped on you it's where your insures would start, the main concern i would have is your boiler wouldn't meet Irish standards 813 and if you were to do this kind of work after the new year and you caused an accident you risk prison and or fine because if the boiler stops calling for heat IE.. the over heat triggers, you are still pumping heat in compromising the safety devices, it's the impact on the gas boiler you have to be aware of and if your wrong it could end in tears, cheerful aren't I , Gary.

demanufactured

I remembere when my mam was getting oil in and we had a back boiler for years before that , the plumber put a non return valve in the system to stop the back boiler heting the oil boiler and vice versa , not sure of the exact setup though.

caspermccormack

I can see your point but surely these are WORST CASE that can happen, If the valve is open to the rads, cyclinder and header tank without power then whats the difference? It can still draw cold water and the hot water that could be boiling can vent up to the cyclinder(heat sink).

caspermccormack

demanufactured wrote: »

I remembere when my mam was getting oil in and we had a back boiler for years before that , the plumber put a non return valve in the system to stop the back boiler heting the oil boiler and vice versa , not sure of the exact setup though.

I know lots of people with duel systems, I'm just looking for the proper connections to do so.

JamesM

caspermccormack wrote: »

I can see your point but surely these are WORST CASE that can happen, If the valve is open to the rads, cyclinder and header tank without power then whats the difference? It can still draw cold water and the hot water that could be boiling can vent up to the cyclinder(heat sink).

Basically, "It's the Rules"

I have just found that I had almost the exact same conversation on this forum over 2 years ago. http://www.boards.ie/vbulletin/showthread.php?t=2054907077
Jim.
Especially read this comment from a plumber:
"as a plumber that in years gone by fitted loads of these systems i would say that JamesM is dead on. At least one house i knew in wicklow had the back wall blown off by a cowboy fitting a dual system. I would say that back boilers are the hardest heating systems to fit properly. Christmas day - big fire + power failure."

There's are lots of different heating installations and i have only seen dual systems with oil, but there's the right way and the wrong way to do things, by rights your boiler should be sized correctly that you do not require boosting system temperature, the heat exchanger on a gas boiler is smaller than on a oil boiler and is less forgiving when over cooked, as i said there's the right way and the wrong way, if you follow manufactures guide lines you can't go wrong and there is no safety issues to be concerned about, so ring pottertons technical helpline 00448706 049 049 and they will give you the heads up, you asked for advice from plumbers, I'm not a plumber or installer, but i am a senior technician/trouble shooter with another boiler manufacture and i get to see the good, the bad and the ugly in installations and what your suggesting would worry me and the only reason i am being so miserable about what your trying to do is i have seen the damage caused when things go wrong, so if you talk to potterton they will confirm what i am saying or tell you I'm a big girls blouse, but a least you will confirm if it's safe which is the main thing, Gary.

caspermccormack

Thanks to both Jim and Gary,

I do understand that it needs water circulating to avoid any damage to the back boiler, I have changed some things on the plans that i had shown earlier in the post and would like your views on the changes, in the event the fire was blazing and the power was lost

PS, I don't think your a big girls blouse Gary, (but you may have issues!):)

yep, gasmans paranoia:eek:

caspermccormack

lol ! did you look at the new diagram?