boiler makes banging noise

[freecountry65]

I have a 3 year old glow worm boiler badged as british gas 330 with a vented cylinder. The boiler makes a loud banging noise after being on for about 15 minutes. The bang is followed by a rushing noise, then the boiler switches itself off. It comes back on almost immediately and will run for another 15 minutes or so before making the same noise. The bang is less freequent if I switch the pump to its highest setting and/or select both hot water and heating. Could it be the heat exchanger is blocked or scaled?
all suggestions welcome.

 

[Agile]

Could the bang be produced by a motor valve closing rather than the boiler?

What motor valve(s) do you have?

Tony

 

[freecountry65]

Hi Tony,
thanks for the suggestion. The noise is definitely coming from the boiler. The three port valve is in an airing cupboard about 2 metres away.

 

[Agile]

Boilers dont generally make a banging noise!

If one did it would usually be because its still heating with insufficient flow to remove the heat.

My suspicion is that the pump may be having its supply interrupted for a short time. I would monitor the supply to the pump during the noise.

Regardless, I doubt that you will be able to identify the problem without professional help and I would go as far as saying that you may need a pretty competent engineer too.

Tony