Potterton Prima F not firing properly.?

samboston

I seem to have the same problem as that described below (sorry to pinch your write up).

My boiler is a Potterton Prima F. I think it might be a 40F.

The boiler can be used to heat both the central heating and the hot water at the same time, or it can be used to heat just the hot water or central heating individually.

97% of the times the following seems to happen.

1) Front boiler thermostat knob set to 3.5 mark.
2) Press boost on programmer/timer unit to turn heating on for 1 hour.
3) Looking through front sight glass, there are sparks between the electrodes, and then you get a small flame (approximately 18 to 25mm ), followed almost immediately by a full flame. I think this is how it should be working. The gas meter is spinning at rapid pace (as expected).

You have the full flame for about 9 to 10 minutes, and all the radiators are warm/hot, and the front outer cover of boiler is hot.
Then the flame goes to the small flame (approximately 18 to 25mm ). The gas meter only spins very slowly. The flame stays at this small size for the rest of the 60 minutes.
I think the flame is supposed to go out completely at this stage, and then light up again to the full flame size as the circulating water takes heat away from the boiler.

If the timer/programmer is switched off and the boiler is allowed to cool say about an hour (although I haven’t timed it), and then if I start from step (1) then I will get the full flame for the first 9 to 10 minutes again, and the whole process is repeated as above.

Any one had this before?
What could be wrong with it.

Thanks
SB