cover off- all fine

[opps]

Hi all

Alpha 240p

A while back, demands for ch and dhw fired up the main jets for about 30 seconds and then nothing, 30 seconds later, up again, and so on.

Powered down the boiler and turned off at the gas switch. Took off cover. No obvious obstructions in burning chamber.

I replaced the cover and tried to relight the pilot. Nothing (fan runs at lower speed, ignition sparks, pilot lights, on releasing the gas switch pilot extinguishes). After hours of trying I initially checked the voltage over the thermocouple- fine. Also continuity over the overheat.

Decided that the gas valve solenoid might be sticking so gave the gas valve a "tap" with a spanner. Hey presto!!! the pilot stays alight.

Still had the original problem though so I decided to spray the insides of the combi with compressed air, also the impellers on the fan and up into the flue. Cleaned air pressure tubes, stuck a pin in the end of the pilot jet to clean it. And cleaned air switch venturi and pipes.

Replaced cover and tried to relight. pilot light still sulking!!! Discovered that pulling the cover forward and allowing air in would allow the pilot to stay alight. replacing the cover but NOT screwing it tight means that all is working as it should be.

AM V CONFUSED. the pressure switch seems to move back and forth but with the cover off (not burning chamber cover) and the tubes removed from the air pressure switch still leaves the pilot light on, is this normal???

With the cover off and dhw firing up and main jets burning the air pressure switch seems to be in the correct positions. obviously cannot see it when the cover is screwed back.

Have used smoke pellets to check the inner of flue and when windy with cover off i can feel the downdraught.

Thanks in advance

Daryl

 

[corgiman]

either the air flow switch is buggered
or the tubes and/or flue is blocked

 

[Gasguru]

A while back, demands for ch and dhw fired up the main jets for about 30 seconds and then nothing, 30 seconds later, up again, and so on

This has nothing to do with the pilot.

In turning off the gas valve and pilot you have probably found a new problem with the boiler.

Decided that the gas valve solenoid might be sticking so gave the gas valve a "tap" with a spanner

Not a good idea to do this - gas valves are delicate, precision made items. Connection on thermocouple/overheat interrupter is poor.

spray the insides of the combi with compressed air, also the impellers on the fan and up into the flue

Compressed air will make little difference to a clogged fan impeller.

replacing the cover but NOT screwing it tight means that all is working as it should be

It is NOT working as it should be it is UNSAFE - do it up tight.

You are way out of your depth - its time to get someone experienced on the boiler to have a look.

 

[opps]

Hi all-Thanks for the advice.

In my defence I must point out that I am not daft enough to use the combi with the cover off- only for testing purposes.

wrt the build up on the fan impellers, the compressed air (through a dusting gun at 10 bar) did blow it all off and now the fan is far more efficient.

I accept that the pilot light ignition problem is likely to be unrelated. it has always been a pig to light, almost since new. The tap to the valve was relatively light (admittedly due to lack of space to swing sledge hammer).

Whilst cleaning out the h/e earlier I decided to sort out the dhw temp sensor which had a scale build up on it, so bad that one of the pins snapped into numerous pieces. have just replaced it (thank god for Part Centre in Harrow).

Strangest thing is though that all is hunky dory now even with the cover screwed tight.

will monitor the situation.

Cannot see how the temp sensor had any influence wrt the cover.

Anyway once again thank you to all of you.

I bow to your superior knowledge.

Daryl