Boiler bangs on turn-off

[NickCollins]

Each time our timer turns the boiler off we then get a loud banging sound from the pipes after the pump turns off after it has run on for a while. I guess the noise is boiling water in the boiler because the water temp doesn't drop fast enough. Any ideas? Faulty pump? Have just had the thermostat changed on the boiler and that seems to make little difference. Both water and radiators running very hot.

 

[chrishutt]

You don't say what boiler or system, but assuming it has pump overrun the possibilities include (1) pump overrun not lasting long enough (2) pump not pumping strongly enough (3) sludge or airlock slowing circulation and (4) 2 port valves shutting and no by-pass to allow pump overrun flow.

 

[NickCollins]

Its a potterton gas boiler heating both water and central heating. I've got the pump on max flow rate. If I turn the boiler off without turning the timer off then I don't get the banging noise. I only get the noise when the timer turns the system off and after the pump has stopped running.

 

[chrishutt]

So it's a Potterton. Any chance of a bit more detail, or is it classified information?

 

[NickCollins]

Sorry not an expert on this as you can probably tell. Potterton Suprima 100

 

[chrishutt]

Do a search on Suprima - you may find the odd thread dealing with similar problems.

 

[NickCollins]

Just been through them all but can't seem to find any that have the banging noise on shutdown

 

[chrishutt]

I've suggested 4 possible faults, but you don't seem to want to investigate them further, so you'd better get a professional heating engineer in.