Faulty printed circuit board (hot water side)

The PCB controls major elements of all boilers including: the fan, pump, gas valve, thermocouple, thermostat, overheat, etc.

Most problems are cumulative with PCB issues. There is a pre-defined sequence of operations for boiler operation which is critical for the proper operation of the boiler.

If any component breaks down or stops working effectively, the knock on effect will stop many components from working. In the first instance it is advisable to work through the ‘sequence of boiler operation’ to eliminate component failures before suspecting the PCB.

If the PCB shows obvious signs that it is faulty (no display, flickering display, error codes, etc.) the PCB should be analysed and potentially replaced if not repairable. PCB’s can be expensive (approximately £400 – £500 for a manufacturers replacement).

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!

Other Issues to check

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