The gas pressure reduces just before the system reaches the set flow temperature with the result that the temperature is not reached and the boiler does not cut out.

RP, December 2009

I will take your advice and many thanks for your help.

RP, December 2009

Then its time to find a registered gas engineer as 3 further checks need to be carried out to find out the faulty part, as one of two parts may be faulty. As the further checks are on gas parts you need a gas safe engineer. But if I am right (not being in front of the boiler) the fix is not a big issue. Kind regards.

RR, December 2009

Yes, the green LED does light up.

RP, December 2009

Does the green L.E.D. indicator light? (right hand side on the control box)

RR, December 2009

RR - Thanks for your interest.
Yes, I think it is doing what it is meant to do but at the wrong time. The gas pressure reduces too soon so that the set temperature is never achieved and the boiler never cuts out. Also, it will not raise the flow temperature above 60 irrespective of the setting.
I have also noticed that water pressure rises to 2.5 bar at 60 which may be related.
RP

RP, December 2009

When you say the gas pressure reduces are you sure the boiler is not only doing what it is designed to do.
The main burner is controled by the moduating gas valve to lower the burner down to a lower flame.

RR, December 2009