Banging combi, but it's off!

[PhilFromYorkshire]

Hi
I'm posting this here because both me and my gas fitter are pretty confused by this.

I'm renovating a house and the combi boiler is banging - loudly but intermittently. However the boiler is switched off at the isolator, which has a glowing light that goes off so I'm a sure as I can be that it's off. Also the upstairs radiators are drained.

It seems very odd that the boiler would bang when it's got no power. The boiler is an Ideal logic+ combi.

The banging seems to be associated with a sound of flowing water. But I'm not running anything - perhaps next door are? The house not on a meter, it's a 1940s ex council semin with a lead supply pipe.

Could the water pressure be dropping when next door turn on a tap and could this cause the bang?

I recorded the bang. I can't include the video in the post, but you can view it here https://1drv.ms/v/s!AgLCmsxNxVV_rq8AerROL_XWiwmtiQ

 

[Hugh Jaleak]

Only thing off top of my head, (other than a Spook), is shared supply, Neighbours washing machine is on, and the suddenly pressure fluctuations as the fill valve opens and closes are causing the noises.

 

[PhilFromYorkshire]

The gas engineer I use just called round. We wondered about similar things.

He's suggested fitting a mini expansion vessel after my stop tap and perhaps a pressure reducer too. He said that might stop the pressure fluctuations.

 

[Madrab]

Has the filling loop/boiler pressure been checked? That doesn't sound like water hammer, more like the pressure release valve banging, if the loop's been left open or is passing

 

[PhilFromYorkshire]

The radiators are currently drained and filling loop disconnected while the bathroom is getting refitted.

 

[kidgreen61]

Does it continue if you isolate the cold feed to the boiler?

 

[PhilFromYorkshire]

Does it continue if you isolate the cold feed to the boiler?

Not sure - it's intermittent but next time it happens I can try isolating it and see if it stops. Great suggestion