I have a Potterton Suprima 80L. When going through the initial conditions check (fault finding guide) I get the following problem:
With mains supply OFF, heating timers OFF, boiler user control (temperature control) set to 0 and gas supply ON all boiler lights are OFF which is correct. Turn mains supply ON and red, green boiler lights and pump come on together for 3 secs which is also correct. Red light is NOT flashing, turn heating timers ON - thermostats calling for heat and green light on boiler begins to flash. All OK to this point which is where the problem arises as follows:

The boiler now fires up (green light on constant and red light off) and continues to burn WITHOUT me turning up the boiler temperature control which is still at 0!

Is the boiler temperature control faulty, or is it the overheat thermostat, or is it something else? (new PCB and thermister fitted within the last few days.........)

Willie, November 2008

When my Potterton fires up it makes quite a noise any ideas what the problem is ?

Bob, March 2014

I had exactly the same conditions.
The plumbers were useless. Most wanted to fit a new boiler!
My information was that a dry joint on the pcb was the problem. Dry joints are produced by incorrect soldering techniques. They may be visible but often are not. The joints near the plug conectors were badly fractured.
The time honoured procedure in the electronics field is to heat up each joint. I avoided those joints connecting chips, which can be damaged by heat. It takes about an hour. Make sure the iron is hot. Hold the iron on the joint. The joint will melt and change shape. Take away the tip of the iron immediately. Don't heat solder on the tip of the iron and let it run onto the joint. Only hold the edges of the board. Static can damage the chip.
I refitted ithe board with very little faith that it would work.
It did work. No flashing red light of death. Wonderful!
Give it a try. You have nothing to lose. Good luck.

Spike Norman, November 2009

i recently changedoverheat stat on boiler but still goin 2 lockout cud it be the pcb bourd

andy, July 2009