Myson / Potterton housewarmer 55 - won't stay lit

My Myson / Potterton Homewarmer 55 back boiler has gone potty! (or is it me!!)

The burner only lights for 5-6 seconds stops for 5-6 seconds then burns again.

Some times it will burn for up to 1 minute with a break of about 30 seconds - this I think is normal.

Rads and Hot water tank get hot - but take time.

Can anyone suggest what might be wrong.

Thanks

Steve

Steve,

I have had the same problem. Firing up for 45 secs then off for 20 secs then repeating this cycle. This happens with either CH or HW or both on this Myson Appollo.

Unfortunately, I have been told different things. Someone said it was a feature of this type of boiler because of the low water content it is heating up. Rang Potterton engineer and he said it was possible for a boiler with this small system to do this, but that didn't actually mean that possibly something wasn't wrong. However, another engineer stated that although the cycling of on/off for this small a system would be true, it should not be this short a cycle !

I have been told it could be worn thermostat, thermostat needs calibrating, thermostat differential not correct, circulation problem, air pressure switch, blocked heat exchanger - all by different people and engineers.

The circuit board, pump and solenoid has been changed but still it does the same thing of this switching on and off every min or so once a temperature has been reached.

I've only moved into the house recently, so would be interested to know why you think burn for 1 min then off for 30 secs is normal. Did this come from a plumber ? Have I therefore wasted money changing these things ?