Question on central heating boiler

akhil · 29 Nov 2010

Hi,

We have a Glow worm 'ultimate' central heating boiler. The problem is it switches on and the flame comes on, the pump starts, and the radiators become very warm. Then after say 30 minutes, the flame goes out (but the pump continues to run.) This on and off behaviour carries on even though the room thermostat setting has not been reached.

I suspect that the PCB in the boiler is to blame. It was replaced for a similar fault 5 years ago. However it costs £100 and I don't want to replace it only to find that doesn't fix the problem.

What do you think is wrong? The only other thing I think it could be is the boiler overheat thermostat. But I think it's very likely to be the PCB.

Thanks.

combispecialist · 29 Nov 2010

if it was overheating u would have to manually reset it to get it back on,ive had a similar problem before and it was a partial blockage in the pilot which caused it to fail to rectify,get a rgi out to clean the pilot

Agile · 29 Nov 2010

That sounds to be normal boiler operation whereby it turns off when the boiler's set flow temperature is reached.

If the boiler stays off for very long in this weather then its oversized or set at too high a heat output.

In cold weather it would typically be set to 80C on the boiler. If the house still does not warm up with that flow temperature the rads are undersized.

Tony

Tibbot · 29 Nov 2010

akhil said:
Then after say 30 minutes, the flame goes out (but the pump continues to run.) This on and off behaviour carries on even though the room thermostat setting has not been reached.

That's how they work, it's called pump overrun. There doesn't seem to be anything wrong.

akhil · 29 Nov 2010

Tibbot said:
akhil said:

Then after say 30 minutes, the flame goes out (but the pump continues to run.) This on and off behaviour carries on even though the room thermostat setting has not been reached.

Click to expand...

That's how they work, it's called pump overrun. There doesn't seem to be anything wrong.

Yes I have also wondered that there might not be anything wrong. But why is the flame constantly switching on and off even though the room thermostat is still on and that temperature hasn't been reached?
My understanding is that the flame has to be on all the time until the room thermostat temperature is reached, at which point the flame goes out. Otherwise is the pump pumping colds water if the boiler goes off?

We have a system where there is a water tank in the loft and that runs into the boiler which then is boiled and pumped around the house.

The house is heating up fine its just that i am concerned about the behaviour.

akhil · 29 Nov 2010

Agile said:
That sounds to be normal boiler operation whereby it turns off when the boiler's set flow temperature is reached.

If the boiler stays off for very long in this weather then its oversized or set at too high a heat output.

In cold weather it would typically be set to 80C on the boiler. If the house still does not warm up with that flow temperature the rads are undersized.

Tony

The house does warm up and the radiators are very warm. It's just odd that it's switching off/on. How can the pump circulate hot water during the time the boiler flame has gone off?

thanks.

combispecialist · 29 Nov 2010

its cos the boilers reached temperature....

akhil · 29 Nov 2010

Could the boiler thermostat be to blame then? It could lose its calibration after many years and that might cause the boiler to switch on and off frequently.

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Question on central heating boiler

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