central heating pump and air in radiators

Andy From Sligo · 09-11-2023 1:36pm #1

hello all. I had to change my Central Heating pump on my outdoor grant boiler the other week because the old one sounded like the bearings were going, it was a shrill on every setting (3 speed pump) .

looking at pumps they seemed a fair old price for a new one but found a fantastic price of one on Amazon at around 30 quid with not bad reviews.

fitted it and it works fine .... in a way .

Trying it at all 3 speeds -

1 speed is lovely, its quiet in operation and no air rushing around in radiators and no fraction of a sound of boiling kettle in the hot press . - but upstairs radiators are not getting hot enough!

2nd speed - its noisy and trapped air is rushing around the radiators (I have tried bleeding as much as I can through each radiator , and pressure relief valve, and the pipe in the hotpress has a radiator type bleeding valve on the pipe) but still there is air bubbling / gushing in the radiators , not constantly but when I listen every now and again and not just in 1 radiator but moving around the radiators , mainly in the downstairs radiators. - also there is a much louder noise of a boiling kettle in the hotpress area.

So, Ideally I would like the number 1 speed of no air in the rads, but with the power of speed 2 where the upstairs radiators get lovely and hot (as hot as the downstairs) .

Just a couple of things to note just in case it has any bearing on the matter:

1.) The pump is on the return pipe inside the outdoor oil boiler unit.

2.) I have unscrewed the pump middle screw after fitting to let the air out.

3.) I have been up in the loft and the CH header tank is full of water and the vent pipe is bent over as it should be at the top of the header tank.

4.) The vent pipe is that of a F&E system

5.) When I changed pump I did not drain down the whole system , I just shut off the 2 shut off valves above and below the pump (these valves do not have the red gate valves , they just have a simple ball valve where you single turn with a pair of molegrips)

I think thats about it - any ideas?

sorry for long post.

whizbang · 11-11-2023 8:16pm

Leave it run for a few days, the air will eventually make its way into the radiators, then you can belled again.

Try to shut off the feed to the hot water tank for a while; often the air just circulates between the boiler and tank, and if there's nothing to trap the air, it just continually stays in the pipes.

Andy From Sligo · 11-11-2023 9:01pm

https://www.boards.ie/discussion/comment/121356244#Comment_121356244

thanks will give it a go. - I cannot find a gate valve for the CH feeder tank so the only way would be to tie up the ballcock , that should be enough shouldnt it?

whizbang · 11-11-2023 9:32pm

Sorry, I meant hot water cylinder in hotpress (if you have one)

Andy From Sligo · 11-11-2023 9:54pm

https://www.boards.ie/discussion/comment/121356512#Comment_121356512

oh right - no gate valves to shut off the CH indirect coil inside the cylinder on my setup for some reason, not even zone valves , thats why I have to keep my CH boiler temp to 60-65c for the radiators and hot tank

Andy From Sligo · 14-11-2023 10:04pm

I am surprised the air in the system is not exiting out of the F&E vent pipe bent over the header tank in the loft - can theses block up?

John.G · 14-11-2023 10:13pm

There shouldn't be much air about since you didnt drain down to install the new pump.

Check that the arrow on the pump body is pointing into the boiler.

Can you post a photo of your pump (with details on label).

Andy From Sligo · 14-11-2023 11:16pm

here is the one I bought - yep the arrow is pointing up. - I didnt like the valves fitted to either side of the pump - they weeped quite a bit when turning the shaft, I wonder if they could have let in air?

Was £35 when i ordered it, gone up in price slightly.

https://www.amazon.co.uk/dp/B08XMGMW6R?psc=1&ref=ppx_pop_dt_b_product_details

These are the valves that were on boiler:

much prefer these type of valves though:

John.G · 14-11-2023 11:50pm

Not sure what you mean by the arrow pointing UP, the arrow on my pump points downwards because its pumping into the bottom (the inlet) of the boiler, up through the boiler and out through the oulet or flow, just be happy that the water is pumping in the correct direction or post a few photos.

Pump speed 2 should really not cause any problems.

I would suggest draining down the system and renewing those isolating valves with the gate type, you could be drawing air into the pump through the old ones, also use rubber gaskets and not the fibre type if this is what you used, you can buy the rubber gaskets separately as the valves tend to come with those fibre type.

Andy From Sligo · 15-11-2023 1:42am

https://www.boards.ie/discussion/comment/121369612#Comment_121369612

Its a grant euroflame outdoor boiler unit:

John.G · 15-11-2023 8:20am

Thanks Andy, that's perfectly clear, so can only suggest the above. I have read some reviewers of that pump saying they had to change idue to noisy operation but that shouldn't cause any air ingress problwms IMO.

Andy From Sligo · 15-11-2023 2:06pm

without having to drain down the system , could I modify the PRV in the boiler with some pipes and elbows (1/2") and put in a AAV and PRV and then open up the original PRV and keep it open an then in theory the AAV should eventually let out the air out of the system?

Or even if they made this self cutting washing machine tap in 3/4 (22mm) that I could put onto the flow pipe and the put a bottle AAV without having to drain down the whole system

John.G · 15-11-2023 4:43pm

I wouldn't move that PRV (safety valve) from its present position on the boiler. I have the same combined cold feed and vent like yours and once any residual air, say after a partial drain down) is vented, takes a few days sometimes, then you will never have another problem, so I think you are taking in air somewhere.,

Andy From Sligo · 15-11-2023 5:15pm

https://www.boards.ie/discussion/comment/121371971#Comment_121371971

yeah it feels something is drawing air somewhere its about a month ago I changed it now and been bleeding the rads for ages now and they still keep gurgling - however only on speed 2 of the pump , on speed 1 of the pump there is no air in the rads. as silly as it sounds could it be the speed of speed 2 on the pump being too powerful and drawaing in air that way?

John.G · 15-11-2023 6:05pm

Presume you have tightened the valve nuts securely onto the pump body. I think you will have to grasp the nettle and renew the isolation valves and reinstall the pump with rubber gaskets.

Any idea of the old pump, make, model and speed setting?

Andy From Sligo · 15-11-2023 6:14pm

https://www.boards.ie/discussion/comment/121372296#Comment_121372296

not yet but I havent thrown it - so when I find it I will take a pic. - that was set to 2 or 3 that much i know/remember.

No leaks of water from the pump isolation valves.

There's no way it being a combined F&E system that the force of the pump (seeing as its on the return) could be sucking in air from the expansion pipe is there maybe?

John.G · 15-11-2023 6:25pm

No way air can be drawn in with the combined setup as long as the cold feed isn't blocked, its a good point though since you only lost a liter or so when changing out the pump, keep draining off water somewhere and ensure the ballcock is making up into the F&E tank.

Andy From Sligo · 15-11-2023 9:55pm

should not this air trapped in the radiators/system make its way up to the vent pipe , over the bend , and then down into the top of the header tank ?

which opens up another question really - when hot water expands in a CH system and it does go up into the vent pipe in the loft , is what exits out of that vent pipe into the header tank - A: just air or b: Air mixed in with the water - and with a combined F&E system does the water in the vent pipe (when its not overheating) just stop at the level of the bottom of the header tank ?

John.G · 15-11-2023 10:23pm

No, "99%" of the expansion takes place up through the cold feed, this should more propery be called the feed and expansion pipe, the area of the feed & expansion tank is X hundreds that of a 3/4ins vent pipe so, because they act as a U tube the level rise in each after expansion will be exactly the same but the vast majority of the expansion volume will be accomodated in the F&E tank, if you bunged off the cold feed with a cold system then the few litres of expanded water will shoot up the vent and into the F&E tank, if the vent pipe wasn't there then you could hardly measure the extra increase in the F&E tank level.

Andy From Sligo · 15-11-2023 11:24pm

https://www.boards.ie/discussion/comment/121373293#Comment_121373293

ah right thank you for that , so that most probably explain the other day when i went up in the attic to check the water in the CE Header tank that the loft was cold but I stuck my fingers in the tank and the water was lukewarm then even though there was no water evident that had come out of the vent pipe that was curved over the tank - so the water and air expands up through the bottom feed of the tank then? - and thats why the water was warm yep?

So works like this yep?:

Andy From Sligo · 15-11-2023 11:51pm

I have rented previous houses (older houses) before with this kind of setup in the attic:

Figure 1.)

Figure 2.)

I actually prefer figure 1.) - but is there any best way out of the 2 or do they both just actually work as good as each other?

Also on houses before the CH pump has been on the Hot out pipe of the boiler and not on the return ... again any better out of the 2 ways apart from that because they have gone on the return its slightly not as hot as the feed so the pump lasts longer (supposedly) apart from that, any other advantages to having pump on the return circuit?

Andy From Sligo · 17-11-2023 12:20am

https://www.boards.ie/discussion/comment/121372296#Comment_121372296

Here is pic of old pump I took off:

And this is pic of the new pump:

John.G · 17-11-2023 12:29am

Both very similar, old one, power, 46,67&100 watts. New 55,70&100 watts.

Whats your next move?, are you removing it and replacing the gaskets with rubber ones?, have you drained some water down to ensure that the cold feed is feeding the system and isn't blocked?.

Andy From Sligo · 17-11-2023 1:40am

I did use the rubber ones yes with the new pump , but the previous pump had rubber and not fibre anyway.

Yesterday I bled a large radiator in downstairs hallway when it was gurgling and cold at top - now normally I would bleed and put a towel underneath bleed valve and wait til water started coming through but yesterday I approached it a different way, I decided to put a bucket under the bleed screw and even though hissing stopped and water came through the valve instead of just shutting up bleed valve I let it run into the bucket for around 5 minutes - in that duration it went from normal stream to spurting and splashing (air in the water presumably) but I still let it run . Afterwards it made a huge difference - still got some air in some radiators but no-where near as much now. So next step do that with every radiator then surely I must eventually get rid of all the air surely in the system in the end . Dont fancy draining down whole system to replace pump valves or whatever not in this weather we are having ... more important to have heat :)

Thanks for your replys and help.

John.G · 17-11-2023 9:33am

And you could hear the F&E tank refilling while draining and is now at its normal level.

Cant offer any more ideas except maybe, spray a bit of soapy water on the isolating valves, especially on the suction side of the pump to see any tell tale signs of air ingress,

Andy From Sligo · 17-11-2023 1:38pm

https://www.boards.ie/discussion/comment/121378659#Comment_121378659

thats a good idea about spraying soapy water on the valve - will try that

when I bled the radiator I could hear a rush of water up in the attic so i presume that was the header tank filling up.

i might put the pump back on speed 1 as well and see how I get on because on speed 2 its quite noisy in the hotpress , sounds like a boing kettle on 2 but not on speed 1

Andy From Sligo · 20-11-2023 10:37pm

Here is what I noticed today - How far up the F&E pipe should the hot water rise to I am wondering , because (I have included a diagram of my setup) on feeling the pipes , the pipes going to the Cylinder and the AAV and to the upstairs radiators were all scalding hot (which is great and as expected) - but the pipe for the Feed & Expansion pipe (indicated in the diagram was stone cold. I was quite surprised at this , I would have thought the hot water would have travelled up (expanded) up that pipe to at least the bottom of the header tank? - no?

Or does that sound like that's normal and the way its supposed to work?

John.G · 21-11-2023 10:11pm

Only around 1.5 to 2L will expand up through the pipe and yes you should feel it getting hot but only while the system contents are getting hot in say 20 minutes or so, it will then cool down.

How are you getting on with your air ingress problems?.

Andy From Sligo · 21-11-2023 11:42pm

https://www.boards.ie/discussion/comment/121397888#Comment_121397888

Ah right thanks for all your helpful advice, when I felt it again (different time) it was hot - so it sounds like that its working as it should then . have gone down to speed 1 now on pump because thats the quitest this pump will run , and (well dont sound like) air in rads any more - but not ideal because upstairs rads are not getting hot like downstairs rads on 1 - I reckon all the rads need balancing up there are some getting really hot and others that are lukewarm and one in en-suit totally cold, taking off the lockshields they (well the ones I have taken off the caps) all look like the lockshields are nearly fully open!! - mind you with the old original pump all the radiators (bar the en-suite) were all getting hot as they should on speed 2.

on the long finger I might either 9on a nice day) : drain down the whole system totally and replace the pump isolating valves (havent tested them with washing up liquid yet , but they dont appear to be leaking) or B.) put the old pump back on and see what happens - it was whining/whirring sound but no air and rush of air sound on speed 2 or C:) take the 2 central heating pumps apart and see how similar they are - if Identical put the motor part from the new pump I bought off amazon onto the body/propellor part of the old pump - just in case the propellor blades on the old pump are better/better designed that the propellor blades on the amazon pump. ... or get another new pump and send this one back to Amazon as faulty (love the way on the box and in the amazon listing it say's 'Low Noise' - it is but only on speed 1)

John.G · 22-11-2023 12:43am

Yes, noisy operation was mentioned in a lot of reviews, at the end of the day you might (depending on what you find when you reinstall your own pump) that you should bite the bullet and spend a few bob on a pump like mine, a 6M Wilo Yonos Pico where yon can incrementally set the pump head in 0.1M steps which can then match your old pump exact output on speed 2, you could write a small book where changing the pump on some open vented systems has given rise to all sorts of problems, for whatever reason.

old pump, power, 46,67&100 watts. New 55,70&100 watts. theoretically, speed2 on both are quite close judging by the power, in watts but as stated above problems can still arise but I can certainly tell you that it wont be a pump problem if you install the Wilo.

Andy From Sligo · 22-11-2023 1:37am

https://www.boards.ie/discussion/comment/121398651#Comment_121398651

Thanks - whats that old saying about buying cheap? - might of guessed when I saw it way more cheaper than a lot of the other pumps.

2 points, if (and it could be a factor) the details on the label on the pump are correct of course (wattage wise per each speed) only way to tell is somehow my plug in digital energy meter one day and really see if the speeds actually do respond to the wattages on the label. Shouldnt be too hard to wire up a patch lead with a 13a socket and a plug for the pump and measure it properly - and 2nd point what is the propellor like in the new pump , if that is of a different design (blade size etc/number of fins) this could impact greatly in operation and noise and effectiveness I would say. It might be worth my time (even though they look exactly identical next to each other) to maybe take bot apart one day (looks like just 4 bolts hold the motor to the propellor chamber and should split) and just compare the 2 propellors if I can get to it - compare the size and shapes of the blades and what they are material they are made of on the new pump versus the one I took off because if there is a difference in that I would say that would affect noise and its operation .

just a shame its all happened in the winter time and I couldnt have done all this in the summer when the heating wasnt in use (well not for radiators anyway)

central heating pump and air in radiators

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