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Discuss Air in heating g system - Already had two plumbers fail to diagnose. in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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29
It certainly looks like that (circled) the cold feed is clear I would think judging by the bubbling, can you just blow down the vent and see does it bubble up in the tank.
Where is the vent teed into your system?.

Just ensure it hasn't been changed and taken off close to some motorized valve or on the wrong side of it.
There also seems to be another pipe directly across from that cold feed on the other side of the tank?? (See video)
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.
 

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ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
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27,332
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
 
Messages
1,630
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
 
Messages
29
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
 
Messages
1,630
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.
 
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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.
 

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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.
 
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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.
 

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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.
 

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