alpha 240e CH combustion on off on off on off

[youky]

Hi all.

When switching on the CH the boiler lights up without any problems and runs until it reaches operating temperature.

Later on when the temperature in CH circuit goes down fan starts (fan light switches from amber to nothing within a second), ignition happens, combustion starts but after 5 seconds, combustion stops and restarts and like this on and off until the temperature is as expected.

DHW is fine it does not happen when asking for hot water and the temperature of hot water produced is good.

So far I have replaced thermistor on CH circuit but problem is still here.

Any ideas?

Thanks in advance for your time and advice.

PS: the boiler had his yearly service done last week by CORGI technician.

 

[Hudd3]

Has the pump gone?.... system heats but because pump doesn't take the heated water away, system thinks the demand is satisfied and switches off until the water cools, when it switches back in.

 

[youky]

Has the pump gone?.... system heats but because pump doesn't take the heated water away, system thinks the demand is satisfied and switches off until the water cools, when it switches back in.

Hi

in this case why would it start in the first place?

 

[Hudd3]

Because the system has no way of knowing if the pump is jammed or not until the water gets too hot. Just take the front screw out of the pump and with a screw driver give the pump a quick spin - should be nice and free.

You will get a small dribble of water coming out but not too much. ...

I am assuming that by start you mean the boiler; if you mean the rads get warm then fair enough, not the pump.

 

[gas4you]

You don't state whether it was doing this before the service, or since?

I would check the fan venturis, aps, although not so probable as DHW runs ok. How long have you left the hot tap on for when testing?

Could be something simple like he has got the minimum and maximum burner pressure set wrong after the service.

 

[youky]

Hi
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HUDD3:
The rads get warm no problems.
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GAS4YOU:
Yes it was doing it before service was done but as system was cold when technician came around and everything works fine when CH is started from cold it is only when maintaining the temperature that this behaviour appears. The technician was unable to replicate the fault because time was running short.

HW works like a charm no problems there.

min and max pressure were not set as they both read within recommended manufacturer values
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thanks for your help all

 

[ChrisR]

Because the system has no way of knowing if the pump is jammed or not until the water gets too hot.

WRONG

 

[youky]

any ideas anyone?

 

[youky]

any ideas anyone?

 

[Agile]

It sounds like a problem associated with the minimum gas pressure causing a lack of flame detection.

Very few people bother to check this on a service and surprisingly few even know how to set it either.

I think you need a competent CORGI as this sounds combustion/gas related!

Tony