Where printed circuit boards do not exhibit any obvious burnt spots (dark staining), cracked joints, blown fuses or any other signs such as water damage, one should never presume it is in full working order. Diminutive components such as resistors, potentiometers, capacitors, transistors and relays can fail at any given time (without any obvious signs), and must never be repaired – replace the board! A good indication when a circuit board is faulty is when all the internal boiler components have been tested in series and proven to be functioning correctly, leaving just the hot water side and/or the central heating side being faulty – it’s that simple!…