Potterton suprima 80l, h/w is fine as is c/h as long as BOTH are on. Once h/w reaches temperature and clicks off c/h is OK for about another 15 minutes then boiler only fires and runs for approx 15 seconds then shuts down cutting out pilot light. New PCB fitted last week, divertor valve checked and operating OK, both thermostats showing 240 volts at boiler when activated and pump running smoothly. Wiring also checked and is exactly as per the Potterton diagram using PWB1, EP3002, MPE322, PTT2 and PRT2 with Grundfos pump.

Can anyone give me any clue as to what is causing this problem?

Willie, November 2008

It's got to be the overheat thermostat on the pipe.The one with the yellow wires
Change it now. very cheap

Peter Gale, December 2009

Hi Ian,
The problem is more than likely with the PCB, I have just changed mine (after the same problem as you) and changed two sensors , parts were £50 PCB and £20 for 2 sensors and everything is fine now.
I bought a repaired pcb which is a fraction of the cost of new from Adlink in Southall.
If you need any help or are local then give me a shout.
shahid.uk@gmail.com
Regards

Shahid Aziz, February 2009

I have a similar problem with this boiler. All works ok until the radiators get hot (5 mins or so), then it cuts out even though the house is not yet warmed up. Manual restart will only work after waiting 15-20 mins. A plumber thought it was due to the water pump, but after installing a new Grundfos 1560, the same problem occurs. Am not as technical as you, but I can tell you it is not the water pump !

Ian, January 2009