Promax 15 HE - explosive ignition

Hi. Need some advice.
Above boiler worked well until some weeks back when it failed and would repeatedly switch to ignition lockout. On well founded advice requested a fixed price repair and an engineer duly came out diagnosed and replaced gas valve and boiler worked fine for a week thereafter. Now there is an occasional loud 'Bang' in the boiler [suspect this is explosive ignition] when it fires up again after having run for some time. First cold start seems to be quiet enough, but subsequent restarts frequently [not always] cause a loud unnerving 'Bang'. 'Bang' sound is even louder when heard outside below the Flue.
Prior to this recent failure - ignition lockout / gas valve replacement - the 'Bang' was fairly quiet and generally not noticeable. But this is no longer the case now.
Is this 'Bang' sound serious ?
And any suggestions on what could be causing it ?
Would appreciate your guidance. Thank you.

Get the guy that fitted the gas valve back if it's only been a week?

He may have not set the gas pressures on the new gas valve properly.

Could be summit else mind you.

jlm is right get him back,a comon problem with the promax is the burner failing and or the electrodes start up should be quite smooth

Hi folks.
Advice noted.
Will arrange for Gas engineer to revisit and investigate.
Many thanks.

Explosive ignition, is a common problem with this type of gas boiler.

as was said above, it is highly likely, (but may well not be) that the pressure on the gas valve needs to be set. The gas valve covers a lot of boilers, including the higher ourput versions of this 15Kw one. They usually come set on maximum gas rate, which may wekk be 30Kw or more.

And it's Not just in the full on position, but when it modulates down to minimum.

These boilers are not supposed to come on full to start with, rather they would come on low, then fire up to maximum, before modulating down again.


Other reasons for explosive ignition are, the spark gap could be needing looked at, or the ignition module ( part of the main circuit board) could be on its way out, producing a weak spark.

All the best with a fix

Hi.
Thank you for this advice.
Problem was fixed by gas valve replacement.
Have a nice day.
regards.

KM321, the gas valve was replaced but the problem continued.

On our advice you called back the engineer.

But what did he do?

Tony