Air in heating g system - Already had two plumbers fail to diagnose.

[Quinla01]

Hi all,

Hoping you can help me out.

We had building work last summer and added a few radiators on both ground first floor. We also replaced our vented hot water system with an unvented hot water system but the heating remains open with a small F&E tank in the loft.

Since the works, when the radiators come on (they are on smart Honeywell Evohome TRVs so open and close on demand) there's a lot of gargling noises from the radiator even on the ground floor. There is also a lot of annoying tapping of pipes around the house that we never had prior to the works. Finally, there is a lot of air in the radiators but I've addressed that by adding the automatic bleed valves although I'm well aware I'm only masking the problem.

I have attached two videos. One is of the F&E tank in the loft showing air coming into it. The other is the recording of the gurgling noise from a ground floor radiator when the TRV opens.

One plumber just suggested the obvious that the radiators need bleeding which I'd already done. I've put automatic bleed valves on all the radiators since I was having to bleed them every other day.

The second plumber was more thorough. He noticed a problem with the installation of the new unvented tank that meant a valve that should be open would close when the boiler overran which he thought could be the cause of the problem. We fixed that but the problem remains. He also tested the water for any contaminants which came back negative (although it did confirm the system has no inhibitor which I need to address) . Finally, he pressure tested it to make sure there are no leaks.

I put a camera on the F&E tank and noticed that every time the boiler fires up (assume also the pump) there is air being pushed into the tank. I have attached a recording if it helps. On the plus side, over 3 days no water was required to top up the tank so hopefully, that means there's no leak.

I'm not sure if it's relevant but one of the new radiators on the ground floor never really heats up. There's no air in it and I removed the TRV to eliminate the possibility of it being locked. The pipe supplying the water get's hot but the pipe exiting the radiator remains lukewarm at best. I've tried opening it all the way up and then closed it slightly each day but it makes no difference. I'm wondering if the is a blockage on the return and I'm wondering if that could be related to the air in the system. My logic is the pump fires up and is immediately met with resistance which causes the burp in the F&E tank. There's no science to my logic so may be complete nonsense.

Lastly, the condensate pipe on the boiler (Worcester bosch 32 CDI about 18 months old) does seem to be dripping constantly when running. My understanding is that it should fill to a specific level and dump the entire lot rather than have a slow drip. Again, not sure if it's related but thought I’d mention it.



Any thoughts?

Thanks in advance

 

[Quinla01]

Any chance of a pic of the problem rad and pipework ?

Sure but I'm not sure there's much to see.

 

[ShaunCorbs]

Ok try this tomorrow close every single radiator via the trvs if they don’t have a trv close a lockshield valve and turn the boiler temp down and turn on the heating let it run for half and hour or so then bleed the radiator

 

[John.g]

I'm pretty sure it's the one I've marked below. Not sure if it's expected but where the pipe joins the system very warm and gets gradually cooler to the point of being room temperature towards the ceiling where it goes into the loft.

Doesn't seem to be any mods to the vent and pump attachment., the vent is a continuation of the boiler flow pipe so will be quite hot for a portion as this is where the expansion takes place.
I would ensure that the vent is clear right up to where its bent over the F&E tank, maybe just blow down it (boiler off) or stick a hose in it and overflow the F&E tank for a few minutes.

Did you look at the F&E tank again and try and see if there is another pipe opposite to the cold feed at the other side of the tank bottom? or maybe its a electrical wire.

One other thing

 

[Quinla01]

Ok try this tomorrow close every single radiator via the trvs if they don’t have a trv close a lockshield valve and turn the boiler temp down and turn on the heating let it run for half and hour or so then bleed the radiator

Will do. Whats the logic there? Thanks

 

[John.g]

Ok try this tomorrow close every single radiator via the trvs if they don’t have a trv close a lockshield valve and turn the boiler temp down and turn on the heating let it run for half and hour or so then bleed the radiator

Systems with a combined feed and vent can be difficult to fill after a complete drain down, I have a gate valve on my cold feed and just barely crack it open to fill the system on the very rare occasions that I do a full drain down but never have any real problems with air in the system when I do this.

 

[ShaunCorbs]

Will do. Whats the logic there? Thanks

could be air locked due to the drain down eg after the nail /screw

 

[Quinla01]

Doesn't seem to be any mods to the vent and pump attachment., the vent is a continuation of the boiler flow pipe so will be quite hot for a portion as this is where the expansion takes place.
I would ensure that the vent is clear right up to where its bent over the F&E tank, maybe just blow down it (boiler off) or stick a hose in it and overflow the F&E tank for a few minutes.

Did you look at the F&E tank again and try and see if there is another pipe opposite to the cold feed at the other side of the tank bottom? or maybe its a electrical wire.

One other thing

I think there is. Look at attached photo. It runs down towards the cold water feed to tank.

 

[John.g]

So, every thing normal enough re F&E tank, mains feed to ballcock and cold feed teed into the up and over vent.

Re the no heating rad, I know you have "proved" no air present but might consider (with boiler off) shutting off L/shield & TRV, remove the blank vent plug on the rad, get a bucket and flush say 3 or 4 litres of water through the rad with TRV only open then shut it and do likewise with L/shield only open, you surely shouldn't have any air in that rad pipework after doing this.

If still problems with gurgling etc, tie up the F&E tank ballcock for a day or two, if the air is just air trapped in the system since refill then the tank level will slowly drop with the continued release of air, if air somehow is being drawn into the system then the F&E tank level should slowly rise.
The bit of bubbling back into the F&E tank mightn't be that significant in view of the close proximity of the pump/vent as its only happening on boiler/pump startup.

 

[Quinla01]

Thanks All, I'm out the house today but will try your recommendations tomorrow. Hopefully, they will help.

 

[Quinla01]

Evening all.
I just wanted to provide a quick update. I followed your guidance on the basis that we may have an airlock in the system. I went a bit further and bought a half inch nipple and fitted a hose attachment on the other side. I did what you guys said regarding heating, closed all the radiators, and then attached the hose to the flow end of the cold radiator and opened it up.There was a load of air in the system. I did the same on the return and again a load of air. I now have a nice hot radiator. Whether it's responsible for the other problems we'll have to wait and see.
Thanks again.

 

[John.g]

Hope the system is back to normal, just a bit curious about your method of purging the system, did you just shut both rad valves, remove one end of rad tails at rad, attach hose to the rad pipe tail , reopen valve and purge back through the flow or whichever you opened?. did you just put a bung in the rad opened end while doing this or did you attach to the rad itself and then purge back through the rad and the opposite tail?
Also some time when you get a chance can you see if this bubbling in the F&E tank has now stopped on pump startup or stop.