Help with CH Boiler

[furyjohn]

Hi guys, I'm hoping someone can give me some independent advice before i call in the pros.

We have a Baxi Combi 80Eco boiler that cuts out intermittently. What happens is that the Overheat (Safety) Thermostat is activated which then prevents the boiler from igniting. Resetting the thermostat solves the problem.

It cut out on Friday, the time before that was about 4 months ago and probably 3 or 4 months again before that and there doesn't appear to be repeatable sequence of events that can recreate the problem, but I'd like to get it sorted.

Anyone have any ideas what the possible causes / solution might be.

Thanks all

furyJohn

 

[Doug B]

Is this when the boiler is in heating or hot water mode?

over heat on heating usually means the water isn`t getting out of the boiler quick enough, so could be the pump, or your radiator water system is sludged up.

But it could be a faulty sender/ stat.

 

[motownmartin]

Do you get any banging or rattling noises, if so it is possibly the pump, if not then it could be a faulty stat.

One other thing, I recently had a problem with my boiler, it cut shortly after starting up, I found out about a month later that it was the gas flow tap had been knocked so it was half closed

 

[furyjohn]

Thanks guys.

We've only really noticed the problem when the heating hasn't come on - although noticed it once when there was no hot water, so can't say for defo which was the cause.

The pump is as quiet as a mouse so i guess it's unlikely that it's the cause.

I drained and refilled (incl inhibitor) the system after the last time it happened and didn't notice any sludge or debris in the drained water - but then again, i wasn't really looking for it.

Faulty sender/stat are looking like the most likely so far then.

I'll check the gas flow tap - we keep towels bedding etc near the boiler so this could have happened.

Can the sender/stat parts be tested ? I mean, if the problem only occurs so infrequently, would they necessarily show as faulty if they were the cause ?

thanks for the help all

[/quote]

 

[Woody Alan]

Zone valve motor dead, if it's a 2 or 3 zone valve system and not a 3 port y valve system. Heat exchanger sludged up.

Alan

 

[furyjohn]

Update:

DougB: It's just cut out again when we were running the bath - plenty of pressure in the water too. The Heating was off so does this make a difference to the diagnosis ?

MowtownMartin: I've checked the gas tap - the only taps are under and slightly inside the boiler so the chances of hitting by accident are next to zero.

Woody Alan: if the Zone valve motor was dead would that not cause the boiler to be permanently off ! ?

 

[Doug B]

John.

It could still be the pump even if it`s quiet.

intermittent faults are the hardest to find, so would suggest a call to Baxi & see how much a service engineer visit would cost, he will have diagnostic equipment to find the fault.

Changing parts to find a fault can soon cost more than a service visit & not rectify the fault.

Doug

 

[Woody Alan]

Woody Alan: if the Zone valve motor was dead would that not cause the boiler to be permanently off ! ?

No, it woud mean that the pump would try to pump hot water (to CH) but it can't get through, so it cuts out on the boiler stat.
If your HW is causing the problem check the diaphragm is not holed.

Alan