Potterton Profile - about 10years old - intermittent firing - pressure switch could be heard clicking in and out - so suspected the Controller board. Removed the 3 capacitors as per previous posts - they all looked OK and behaved like capacitors should when tested on a small multimeter - put them back, soldering carefully - same problem as before - so made the trip to Maplins - 2x 22uF 63v and one 4.7uF 63v - soldered them in instead and it works perfectly! Magic. The capacitors are obviously breaking down at the 50v circuit voltage - so a higher voltage rating would be a better long-life design solution. The resistor R15 between the relay and the pressure switch connector block was looking seriously overheated - so changed that as well. Black-brown-yellow = 100K-ohms, looks as tho' it may have 240 across it - so with i=E/R that makes 2.4mA or 567mW i.e. over 1/2 watt - no wonder the little 1/10 watt component looked frazzled. Its a pity these circuit designers don't do their job properly - or perhaps it is deliberate built-in obsolescence. If it was fitted to a Toyota, we'd have a global product recall and all get our money back.
Roger Forshaw, Romsey Hants, February 2010
