The 407677 pcb in my potterton profile 40 is faulty ( thanks to this site for finding answers to symptoms). I can get a service exchange, but need the old board off intact. It seems to be held in by 4 plastic lugs. I pulled quite hard against these, and tried squeezing them in on the top, but the board resists coming away. I don't want to use excessive force and break it - howz-it-done?

Also, having diagnosed that the board has either faulty electrolytics or dry solder joints and needs servicing, I have also found that I can make the boiler fire by holding the reset button in. Its not clear if this is part of the pcb fault, or a compound fault with the overheat cut-off. The overheat has not clicked out, and if the boiler is down to stand by pilot, it fires only while the button is held under finger pressure, going back to pilot as soon as pressure is removed from the reset switch. Is this symptomatic of a compound problem in that the overheat is faulty. Is there a test? The wiring diagram indicates that the switch is normally on, so bypassing the cut-off by hot wiring the two brown leads on the cut-off should provide a permanent on, and prove the switch as good or faulty. Is this a right hypothesis?

Jerry, November 2007

Thanks, PCB came away with a bit more effort. Used a unit of EBay, sub £50 and less than half Potterton's price. New unit worked fine, so it looks like the overheat was a symptom of the board faults. Thanks to Jon11 for his advice.

Note to anyone with a boiler using this PCB, if it repeatedly attempts to light but fails many times before lighting - that the advice to tap the side of it while in the start up cycle, does work, it lights every time. How-ever, this is just proof of a bad board. The DIY repair is check for dry solder joints and replace the electrolytic capacitors. I didn't attempt it, going for a replacement board, but it seems these are the common failure faults on most boards.

Jerry

Jerry, November 2007

If the boiler fires when you press overheat I would say that the overheat is faulty. You are right, If you bridge the 2 brown wires and it works that proves it must be the overheat stat & nothing to do with the pcb.
(To remove pcb squeeze the top of the plastic lugs & lever up gently one corner at a time)

jon11, November 2007