Trapped air in heating system

[Chippy99]

Please can someone offer some advice?

I have an unvented hot water and central heading system and a few weeks ago, had the hot water tank replaced.

Since then, I get loud knocking and glugging sounds when the pump is running, due to air circulating around the system.

However, the symptoms are puzzling: With only the hot water on, it's terrible - constant, loud, glugs, knocks and bumps.. But when the central heating is on as well, it'quitens down after a minute or two and is hardly a problem. It seems the trapped air is getting in somewhere in the loop between the boiler an the hot water tank heat exchanger?

I would have expected by now the air to have found its way to the top of one of the rads and for me to be able to bleed it. But no - all the rads are piping hot and full of water - no air to be found.

So how do I get this residual air out of the system? The hot water comes on early every morning and the racket wakes me up, it's so noisy.

I'd be grateful for any tips or advice. Thanks.

 

[dilalio]

There should be a manual or automatic air vent on the highest point of the system. Have a look for one near the highest heating tap-in on the cylinder.
Anything beyond that needs to be evaluated by a g3 installer - have you called the installer?

 

[Chippy99]

Thanks - no, haven't called the installer yet. It's BG and I am usually very impressed with whatever random bloke they send out.

The only value or vent I can see (other than the pressure and temperature safety valves for the tank itself) is on the left. I think it's where you top the system up with inhibitor or whatever. Is that the one you mean? The hot inlet from the boiler is next to it on the left; the cold return is middle bottom.

I just noticed it's very slightly wet, and there's some crud around it, so it looks like it's leaking very slightly.

 

[dilalio]

That’s an AAV (auto air vent) and it should allow air to escape but not water.
Give it a clean and dry it out but it probably needs replacing.
Is the cylinder the highest point of the system? Where is it? Are there rads above it? Air should have worked itself out of the coil by now. EV may need repressurising. Discharge doesn’t look great either. Call BG back out.

 

[Chippy99]

The cylinder is upstairs but I would say not the highest point since we have vertical rads in the bathrooms which are higher at the top than the hot water inlet and return on the tank.

Should the bleed valve be installed so that it is at highest point?

And how do I clean it and dry it out? Would this need the system draining down? (In which case it's definitely something I'd get BG to do). My only concern is that there's a £60 callout excess on my policy and I'm unemployed so don't really want to toss £60 away.

Thanks for your advice by the way - much appreciated.

 

[dilalio]

Well, if they installed the new cylinder they should have spotted the AAV problem if it was an issue at the time. They should also have got all the air out... Id ring them to discuss - and make it clear you don’t expect the £60 charge.

 

[dilalio]

AAV is fine where it is. They should have made all checks before leaving you. Was it banging when they finished up or were you not there?

 

[ianmcd]

I personally dont think that trapped air is the problem, that is a very poor installation

 

[dilalio]

I personally dont think that trapped air is the problem, that is a very poor installation

I have to agree - it’s not great and possibly not to MI’s!

 

[Chippy99]

Well, if they installed the new cylinder they should have spotted the AAV problem if it was an issue at the time. They should also have got all the air out... Id ring them to discuss - and make it clear you don’t expect the £60 charge.

Yes, they should. They re-plumbed all the pipework to install the new cylinder, so they at the same time move the AAV, so it was either working fine and they broke it, or it wasn't and should have been replaced at the time. They told me the air in the system would work its way out in a day or so (so I let them leave with it as it is) but it's not got any better in about a month.

So yes, I'll ring them and get them out again.

Should the AAV be positioned higher up though? I can't remember where it was before, with the old tank.

Thanks again.

 

[Chippy99]

I personally dont think that trapped air is the problem, that is a very poor installation

I have to agree - it’s not great and possibly not to MI’s!

Please can you explain why? The guy who fitted it has worked for BG for 40 years and they reckoned he's the one guy in the area who does the unvented installs. He did my neighbours a few years ago as well, when their tank failed. I think he's the best they've got!

Is there anything I should be concerned about?

There's definitely air going around the system, btw. There's no doubt about it.

 

[dilalio]

Get them to send a different engineer and ask him what parts of the install are not to MI’s. Look in the manual yourself - you’ll soon see some issues!

That immersion heater is going to be fun to try and replace

 

[Chippy99]

Get them to send a different engineer and ask him what parts of the install are not to MI’s. Look in the manual yourself - you’ll soon see some issues!

That immersion heater is going to be fun to try and replace

I haven't spotted anything that the MI's say shouldn't be done. Are you just guessing, or are you thinking of something specific? I agree about the immersion heater, but honestly the waste water pipe work is all pretty trivial to move if needed. The rather bizarre "up and over" cold fill is because the relief valve needs to flow down to the tundish on the left.

I appreciate it might not be cosmetically marvellous, but I guess that's one of the consequences of replacing one tank with another one with completely different connection locations.

So I can live with the bodge job appearance. What I cannot tolerate is a faulty install that's going to give me years of trouble. I have to say I wasn't too impressed when he drained the (new) tank contrary to the instructions on the side which Gledhill say MUST be followed when draining the tank!

EDIT: OK, so I've just found that the max distance from the p&t relief valve to the tundish is supposed to be at most 600mm and it's quite a lot more than that - perhaps 1m.

Does this REALLY matter? To remedy this would need the install redoing (assuming I could persuade BG to do it) and I can honestly not be bothered with the hassle unless it's absolutely essential.

 

[ianmcd]

Please can you explain why? The guy who fitted it has worked for BG for 40 years and they reckoned he's the one guy in the area who does the unvented installs. He did my neighbours a few years ago as well, when their tank failed. I think he's the best they've got!

Is there anything I should be concerned about?

There's definitely air going around the system, btw. There's no doubt about it.

A sealed system is exactly that, it is sealed, not unknown to get air trapped in a sealed system but not common, if the highest radiators are heating and not cold at the top and constantly needing bled then it is unlikely to be air, as @dilalio says changing that immersion if required will be interesting, unfortunately just because BG use your installer does not mean they are any good, call BG and tell them that you are asking Gledhill for a warranty call, Gledhill will say that if it is an installation fault then there will be a charge for the call-out, tell BG that they will be paying the charge , that will get them moving, in your pic at the bottom there is a valve with a red handle, open that fully and see if the problem stops.

 

[Chippy99]

It's definitely air.

BG didn't use my installer. BG used their installer - I have never met the bloke nor heard of him before.

I am very reluctant (i.e. not going) to get Gledhill out and getting into a row with BG about it. I am unemployed and have bigger fish to fry than this right now, but thanks for the suggestion anyway.

The red value at the bottom is the same as on the previous install. As far as I can tell it's a connection between the radiatator circuit and the hot water heater circuit - is that right? I guess the value is there to balance the flow between the two, but I was never sure and never know what position its supposed to be set to.

Can you explain further please? Why would opening it fully fix the air issue?