Just a note to all of you lucky fellow Potterton Suprima owners coming home randomly to a cold house and no hot water. We have suffered the above very occasionally for 2 years, then noticed that the house took ages to warm up this winter: when you went to the bolier the boiler may have been off for no apparent reason as there was a "call for heat" that it wasn't responding to. During this time the boiler only occasionally "locked out" completely. The problem gradually got worse until 2 weeks ago the bolier was switching itself off every few minutes. Bolier serviced regularly; pump, valves etc all working. This site told me that the PCB was probably the issue so being a tight git a bought a refurbished one for £49 from sarumlady on ebay(great service); has been in place for 10days with absolutely no problems; i wish I'd taken the chance two years ago as we must have wasted more than £49 of gas! Have a look at your old PCB first before ordering; switch the power off at the mains; it's only fixed with one screw on my Suprima 60 and hinges forward; mine was darker brown in the middle of the board. Fitting; I'm not a great diy-er but putting the new one in took 20mins; wear earth strap to protect the new PCB from the static in you, switch off at mains, take some digital pictures of the old one if you're worried about getting the wiring wrong (you cant anyway as the wires plug into the board), and (if your reset button doesn't protrude) cut a small hole in the brown film on the front of the boiler where the previously useless reset button was. (oh and don't fiddle with anything else on the bolier or you're a prat.) Alternatively, buy the board yourself and get a professional to fit it.