The central heating pump is supposed to continue to run for approx 8 minutes after the timed cycle to cool the heater matrix. In my case the pump runs continuously but if you tap the PCB it switches the pump off as it should. I have replaced the PCB and everything works fine but I would like a circuit diagram of the PCB if one is available to try to repair the original.

Mr R. Dyson, February 2011

While you wait for a circuit diagram you might consider changing all the electrolytic capacitors on the board - they tend to fail and particularly so in a warm environment...

An interesting article about a Potterton PCB here...

http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler

Good luck...

Peccavi, February 2011