Potterton Suprima 50 - strange problem

[missp]

Hello,

Can anyone help?

I have a Potterton Suprima 50 (riddled with probs I see from these pages...).. but anyway, I have been running the hot water without any problems all summer - the boiler and pump appear to have been working fine. However, just recently I had to set the timer for the heating to come on as well.

What is weird is that intermittently - but more often than not, the boiler will not fire when just the heating is called for. But, if both heating and water are called, then the whole system works okay. As soon as the water is switched off, but heating is still on, the boiler shuts down and the radiators cool down. The only way to have heating is to run the hot water as well.

Any ideas? This boiler already had a new PCB in January this year.. at great expense.

Thanks in advance

 

[MANDATE]

I would suspect the motorised valve spindle possibley stuck on 'hot water ' or 'mid positon'
I would certainly remove the motor and turn the spindle by hand a few time to make sure its free with a little helping of WD 40.
I would also ensure the motor turns to the correct position ie 'hot water or 'central heating' or both( mid positon)