Banging noise about 20 minutes after heating/hot water goes off

[taylori]

Hello,

Last year we were having various boiler issues with a 12 year old potterton HE boiler. One of which was a loud explosive banging noise about 20/30 mintes after the system switched off. As a result of this, and a few other issues, we had the boiler replaced at Christmas with a Worcester Greenstar 15ri. the boiler and system operates fine, plenty heat and hot water. However, the banging noise has remained just the same as with the previous boiler. I've requested the engineers come back and look at it again, but as it only happens last thing at night, i'm not sure they'll be able to do anything as I cant demonstrate the problem. It was also an issue before they got involved.

What can cause this issue? Could it be to do with the heat pumps under the cylinder or the cylinder itself? we live in a hard water area, though the system has been drained and treated twice in the last 12 months.

Any advice is appreciated.

 

[stevetheplumber]

some thing that only happens late at night is a nightmare to diagnose,and as this was a problem with both boilers it must be system related. As a first step i would remove all the trv heads for 24 hours see if that makes any difference.Check any motorised valves are flowing the right way
can you isolate the area the noise is comming from?

 

[taylori]

Thanks Steve. I will look at removing the TRV heads. I owuld have said the noise sounded like it could be from the flue originally, but that was when we've been downstairs. We were in bed last night and it sounded more central, so could be the cylinder cupboard. We did have one of the pumps replaced last year, the one for the heating. If this was on the wrong way, could it be the cause of this problem?

 

[Radioman]

I had this many years ago. It only happened after a long run of the boiler, say 4 plus hours. The heating would go off on the timer and about 5 min later it sounded like a poltergeist in the walls. It turned out that the water in the pipe work in and out of the boiler was boiling, creating steam, which could not get out unless it pushed back through the system. An old school heating engineer put a gizmo on the controller that ran the pump until the temp dropped below 50 deg. Never had another noise for 15 years.

 

[bonkersboiler]

Is it possible that a heating pipe is a tight fit as it passes through joists? You can then get noises as the pipe cools and contracts.