Potterton Suprima 100 Boiler makes loud noise on ignition

[dominoman]

My boiler (old style - non condensing) works well, but when it turns on it makes a very loud banging noise, often loud enough to shake the walls two stories away.

It sounds worrying.

I called a gas engineer and he said not to worry and it was just late ignition of the gas, and he said he would come around and fit a new ignition once he got the part.

That was two weeks ago and since then it has got worse, so yesterday i removed the ignitor, cleaned it in white spirit and checked the gap was OK. It made no difference at all.

Is there anything else i should check, and should i be worried?

 

[45yearsagasman]

That was two weeks ago and since then it has got worse, so yesterday i removed the ignitor, cleaned it in white spirit and checked the gap was OK. It made no difference at all.

Is there anything else i should check, and should i be worried?

Amateurs should not be trying to cure ignition faults on gas boilers. Get it properly repaired. Should you be worried? I'll let you decide.

 

[dominoman]

I have now had the ignition checked and there is no problem there.

The loud bang is nothing to do with the gas ignition. It seems to be to do with a water hammer effect, or perhaps air that is expanding in the system.

It only happens sometimes, and seems to be when the boiler and pump restarts after having been off for a while.

Any ideas what I can do. I have called plumbers / GSI three times so far and each time something was replaced but the problem is still there.

 

[dominoman]

UPDATE - I've been watching the boiler and pump. What seems to happen is that after around 20 mins or so the pump stops. At that point the boiler is still heating the water and it makes the loud bang noise (presumably from overheating and turning to steam).

So, the question becomes why does my pump occassionally turn off while the boiler is still heating water? The pump itself is new so it isn't that (and it had started happening with the old pump).

Could this be a PCB problem? Or a problem with the temperature sensor in the boiler. I don't know enough about what is supposed to turn the pump on or off.

 

[45yearsagasman]

Pump is pcb controlled.

 

[dominoman]

Pump is pcb controlled.

Thanks. I could replace the PCB but before I do that is it worth replacing the temperature sensor? Or the overheat sensor. What do each of these do?

If that wasn't working could it cause the water to get too hot and then the pump would shut down for a bit.

It seems strange that the system works fine most of the time, but just every now and the the pump switches off for a short time.

 

[dominoman]

Does anyone have any advice on what I should try before replacing the PCB? The boiler works fine, and there is no problem with the ignition. Just the loud bang noise that happens every 30 mins or so.

 

[45yearsagasman]

Intermittent noises are almost impossible to diagnose from behind a keyboard. A site visit will be required to properly identify fault.

 

[dominoman]

More investigation today from watching the boiler. Once it has been on for 30-40 mins from cold gas switches off (as it at max temperature)

Then a few minutes later the gas switches on again, but just for a couple of seconds while that happens the pump is off. So get a bang as no water is moving through the heat exchanger.

 

[dominoman]

This loud bang noise continues. Last night my Gas Safe boiler man came around and spent a long time going through diagnostics and testing everything.

My previous theory was all wrong. It turns out it is definitely caused by explosive ignition.

The strange thing is that it happens only when the boiler is already hot. Never from cold.

He checked:
- Electrodes and spark. All fine and sparking strongly.
- Gas pressure / Gas valve. All fine. Gas pressure starts lowish and then increases once the flame ignites, which is as expected
- Fan. Starts a few seconds before the sparks and gas starts, as expected, to clear out any old gas in the chamber.
- Pump. All fine. Runs as expected.
- PCB. It's a new replacement version and seems to be behaving as expected.

It's a real mystery. The boiler always fires absolutely fine when the boiler is cold, but once it gets up to full temperature it re-lights with the loud explosive bang almost every time.

In the end the engineer replaced the ignition cables to the electrodes, just in case they were occassionally shorting. He admitted that he thought that was unlikely - but by that point was out of other ideas.

I've got full confidence in my boiler man. He's really good and worked through every option in turn. But he's stumped.

Has anyone got any other ideas of what could be causing it? What could he try next?

 

[Tibbot]

If you're happy to stick with your gas man, ask him to join the RGI section of this forum. People there may be able to offer detailed advice.