Combi boiler makes loud bang

[Benji24]

Hi. I have a Worcester combi boiler. I had it's annual service done a couple of weeks ago. The electrodes needed replacing which they did. Since then, when the hot water is turned on (not every time) the boiler make a loud bang.
I called the plumber back today and they replaced the electrodes with another new part. Everything seemed good but just turned on hot tap and heard the noise again.
Please could someone advise on what they feel it could be.
Thank you.

 

[Madrab]

If it's a bang on lighting then it may be explosive (delayed) ignition, needs sorted properly before it damages the boiler. Record it doing it, to show them, if it's intermittent.

 

[Benji24]

Hi. Thank you. I did record the bang and showed it to them. They didn't mention anything about a delayed ignition. They replaced the electrodes and tightened up some connections. They wanted to see it happen whilst there but typically it didn't do it. I will call them again. Thank you.

 

[Harry Bloomfield]

They didn't mention anything about a delayed ignition.

It just where the level of gas builds, up in level, without being ignited, then suddenly ignition occurs of a much larger volume than it should - that's when you hear the bang.

 

[Benji24]

Thank you. Yes that sounds like what happens. It never used to do this, it's only since it has been serviced and the electrodes have been replaced. Still something to get sorted though?

 

[Harry Bloomfield]

Thank you. Yes that sounds like what happens. It never used to do this, it's only since it has been serviced and the electrodes have been replaced. Still something to get sorted though?

Yep, get them back to it. The sudden gas explosion can damage your boiler. Apart from the ignition, I would be checking the burner too - the burner, may not be putting the gas where it's needed, near the ignition electrode.