Boiler Ignites with Bang

riph72 · 24 Jan 2006

Hello,
I recently had my boiler serviced (by a proper gas installer) and since that day whenever the boiler lights, rather than just lighting, it seems to light with a bit of a bang, as if too much gas is getting in prior to ignition?
It really is quite a thump, it sounds as if the thing is going to blow itself apart sometimes!
So, does anyone know what the problem might be and what I can do about it?
I\\\'ve tried to contact the guy who serviced it and he is proving rather hard to get hold of (I guess he knows there will be no money in it for him) :-/
Regards,
Richard.

meldrew's_mate · 24 Jan 2006

You didn't say which boiler you have and that is relevant.

If it has a permanent pilot it COULD have been set too low and burner cross lighting is delayed leading to a build-up of unburnt gas in the chamber before it finally goes off with a bang.
Similarly if the burner pressure is too low.
Similarly if the "soft-start" on some gas valves has been set too slow.
Similarly if the ignition electrode gap (on spark ignited) is too large or too small.

Etc., etc., etc..

Please elaborate on make & model.

snowgatehead · 24 Jan 2006

I wouldent like ot comment on the gas, but I did have a similer problem at my old house.

The boiler would run ok for a time, and then for a short period the boiler would start banging (quite nasty).

It turned out that the circulation pump was intermittently stalling, hence the water in the heat exchanger was vapourizing.

The so called plumber who serviced the system the month before must have f****d about with it or somthing!!

anyway, The heat exchanger had to be replaced at around £300, as it had split due to this.

Word of advice, check the pump is circulating at boiler startup, if thats ok, there could be air in the system (unlikely, but worth mentioning)

riph72 · 24 Jan 2006

meldrew's_mate said:
You didn't say which boiler you have and that is relevant.

If it has a permanent pilot it COULD have been set too low and burner cross lighting is delayed leading to a build-up of unburnt gas in the chamber before it finally goes off with a bang.
Similarly if the burner pressure is too low.
Similarly if the "soft-start" on some gas valves has been set too slow.
Similarly if the ignition electrode gap (on spark ignited) is too large or too small.

Etc., etc., etc..

Please elaborate on make & model.

I am in work right now so can't say which boiler I have, I will check tonight and let you know, thanks.

In the meantime, I think it does have a permanent pilot. I can say that it was ok before the service! Are any of these things you suggest likely to have been adjusted during a regular service?

dal5band · 24 Jan 2006

I have a potterton kingfisher floor mounted and it was prone to go off with a bang when new about 7 years ago. As far as I can see, the burner holes are not near enough to the pilot and the gas takes a little longer to reach the pilot and by that time gas has built up in the chamber and it goes off with a bang. It seems to have settled down with age.
Maybe with yours being all cleaned out etc and the pilot adjusted down the ignition isn't smooth. Could be the pilot is too low or has just been moved a fration so it dosn't point towards the nearest burner holes.

riph72 · 24 Jan 2006

dal5band said:
I have a potterton kingfisher floor mounted and it was prone to go off with a bang when new about 7 years ago. As far as I can see, the burner holes are not near enough to the pilot and the gas takes a little longer to reach the pilot and by that time gas has built up in the chamber and it goes off with a bang. It seems to have settled down with age.
Maybe with yours being all cleaned out etc and the pilot adjusted down the ignition isn't smooth. Could be the pilot is too low or has just been moved a fration so it dosn't point towards the nearest burner holes.

I think the solution is going to be somewhere along these lines, I don't know much about it (well, next to nothing actually) but this sounds plausible to me.

I don't know if this is helpful, but I think it lights with slightly less violence when it's warm? I think it seems to be worse when starting "from cold", i.e. first time on for hours. I COULD be imagining this though!

ollski · 24 Jan 2006

snowgatehead said:
The so called plumber who serviced the system the month before must have f****d about with it or somthing!!

lol, why? pumps go all the time.

Jeronimo · 24 Jan 2006

If you have a boiler with a combustion chamber made up of parts bolted together, look for loose bolting allowing gas to escape from the chamber on start-up.

I had this on my Baxi Barcelona. The top and bottom covers of the combustion box were loose. When the boiler lit up it shook the whole casing with a real whooomp

Tightening the screws fixed it.

Jerry

riph72 · 24 Jan 2006

meldrew's_mate said:
You didn't say which boiler you have and that is relevant.

If it has a permanent pilot it COULD have been set too low and burner cross lighting is delayed leading to a build-up of unburnt gas in the chamber before it finally goes off with a bang.
Similarly if the burner pressure is too low.
Similarly if the "soft-start" on some gas valves has been set too slow.
Similarly if the ignition electrode gap (on spark ignited) is too large or too small.

Etc., etc., etc..

Please elaborate on make & model.

It's a Glowworm Economy Plus.

Any help?

leaks · 26 Jan 2006

Nuff said

riph72 · 26 Jan 2006

leaks said:
Nuff said

Jeronimo · 27 Jan 2006

Apparently a comment on your (?) choice of boiler.

Have you determined whether or not there is a leakage path out of your comustion box.

Note that the lighting up of the flame will inevitably produce a pressure pulse insde, most of which should escape through the flue. With my Baxi, there was a leakage path causing gas to exit the combustion chamber in sufficient amount to shake the boiler casing quite alarmingly. Tightening everthing up eliminated this.

Check it out.

Jerry

riph72 · 27 Jan 2006

Jeronimo said:
Apparently a comment on your (?) choice of boiler.

Have you determined whether or not there is a leakage path out of your comustion box.

Note that the lighting up of the flame will inevitably produce a pressure pulse insde, most of which should escape through the flue. With my Baxi, there was a leakage path causing gas to exit the combustion chamber in sufficient amount to shake the boiler casing quite alarmingly. Tightening everthing up eliminated this.

Check it out.

Jerry

The engineer is supposed to be coming tomorrow, if he doesn't turn up or something, I shall investigate!

Cheers for the help everyone.

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Boiler Ignites with Bang

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