Apollo 15/30 electrical bang! (Sounds like)

[Livy]

Hi
Anyone shed light on a problem I have with my boiler. When the thermostat temp is reached, wall stat or boiler, high or low, the burners will turn off and the pump overrun will kick in. Around about 5 sec later, give or take, there will be what I can only describe as loud electrical bang or when a balloon is popped. There is no burning smell or obvious flash. It does not happen every time, may be once or twice a week.
The parts I've replaced so far are: high and low stat, pump overrun stat, over heat stat and thermo coupling. The only thing I can think of is a dodgy gas valve which I know is expensive and requires a Gas safe engineer. Or would a faulty suppressor have the same effect?
For now the boiler is turned off and pilot light extinguished. Thank God for the immersion heater. Just in case you are wondering, the noise started before I replaced the parts.

 

[Dan Robinson]

Just about everything you have done so far has required an RGI. Might be an idea to get one in before you throw more unneeded parts at the boiler .

 

[garethgas]

Or you could just remove the suppressor, that's usually the culprit.

 

[Livy]

Or you could just remove the suppressor, that's usually the culprit.

Hi garethgas, just thought i'd let you know. Since disconnecting the suppressor about six weeks ago there has been no ballon like popping sounds. Your suggestion was much appreciated. Thanks.

 

[Agile]

So now he is using the boiler without a supressor!

Someone advise the radiotelecoms agency please!