Noise from CH pump and boiler occasional overheat

10 Mar 2004
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United Kingdom

Our CH is has been causing some problems for a while now and I don't seem to be able to get to the bottom of it. There are two problems that may be related:-

Prob 1
We have a Baxi Solo 3 conventional boiler (less than 1 year old) that occasionally goes into overheat and shuts down until reset. This will happen 2 to 3 times a week now the cold weather is here. In the summer it was about once every two weeks.

Prob 2
There is a deep thrumming noise coming from the CH pump - loud enough to wake the family in the morning. This sound appears no matter what the speed of the pump is set to.

All radiators get hot with no cold patches. We have had a plumber/heat eng look at the system and he said air was getting in since the heating overflow pipe was not in the expansion tank. He extended the end of the pipe so it reached below the water level in the expanion tank to stop air being sucked into the system.

I have tried to bleed all radiators and just get water out. When the CH shuts down I cannot hear water bubbles or gurgling as air settles. However, when the boiler stops and the pump continues in overrun the thrumming sound continues.

Could this be air in the system (if so how can I get rid of it) or a pump whose bearings are going - or something else entirely?

Thanks in advance
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He extended the end of the pipe so it reached below the water level in the expansion tank to stop air being sucked into the system.
That's a highly irregular and suspect thing to do. Given that the vent pipe is an important safety device, anything that compromises its function is potentially dangerous.

My initial thoughts are that the arrangement might result in water being sucked from the tank down the vent or feed pipe, and then returning to the tank via the feed or vent pipe. Such circulation will have all sorts of damaging consequences including accelerated corrosion and weakened circulation through heating circuits.

I should look around for a competent heating engineer if I were you. What's more, I don't think the idiot who did the above should be let loose on heating systems, so if he is Corgi registered or a member of IPHE you might want to report him.

Thinking about it, does that also mean the system would be difficult to drain as the expansion pipe being submerged in the F&E tank would create a vacuum?
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No, atmospheric pressure on the water in the F&E will send it down the pipes as you drain out of the bottom. after a gallon or two the pipes in the F&E will be sucking in air as usual.

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