boiler makes loud bang

[freecountry65]

I have a glow worm 30hxi system boiler badged as british gas 330. The heating is conventional vented with a hot water cylinder. I have a combined feed and vent, drayton 3-port valve and grundfos pump. The problem is that the boiler makes a loud bang if only heating is selected - and I mean it's LOUD! sounds like the thing is going to jump off the wall. It makes it a lot less often if heating and hot water are selected together OR if the pump is turned up to its higest setting. And another thing. It sounds to me as though the boiler is putting air into the system. If I listen to the pump I can hear a rush of air bubbles as the boiler kicks in.
I'm baffled as to what's causing this noise - as was an engineer who came out to service it.
any ideas?

 

[bhm1712]

this is what gets me about so called heating engineers - how can they call themselves engineers if they get baffled by something??? have they ever done fault finding and do they actually know anything about boilers and controls??

when does it make the banging noise? is it when the heating first comes on, or numerous times during a heating period??

have you felt the flow and return pipes as the noise is happening? and the pump? does the bang eminate from either of those? or is it from within the boiler casing?

 

[cross thread]

zone or diverter valve ,if it constantly makes the noise it should be easy to trace

 

[bhm1712]

gordongas- i agree.

Sounds like a valve related issue here.

are the motorised valve/s local to the boiler?

 

[freecountry65]

Thanks guys for the swift replies. The noise is definitely coming from inside the boiler casing. The 3-port valve is 3 metres away in a cupboard. I will try to link a video to this page.

 

[gas_man_gaz]

sound like a fault with the ignition to me

 

[gaswizzard]

Possibly requires burner setting up (CO2).

 

[BARNY78BG]

hi there, cant be issue with boiler as that operates in an equal way to when either heating or hot water is called for, so i agree it must be a valve issue!

 

[freecountry65]

if you copy and paste this

kissit65

into google it should lead you to a video I've made of the boiler banging.

 

[bhm1712]

here is the link guys

http://www.youtube.com/watch?v=zT9GztNBdGU&context=C3e9848aADOEgsToPDskL0OHqzu2TIiuUxM9x0De5u

does sound odd, the bang occurs right before the fan starts up.

 

[BARNY78BG]

HI GUYS, CENTRAL HEATING CONTROLS OPERATE BEFORE BOILER SO AGIAN WITHOUT BEING THERE WOULD SUSPECT VALVE