Technical description
Fan keeps running: a. electrical connections mixed up. b. electrical connections interrupted.
What causes this fault?
This fault occurs when the boiler's main internal computer loses track of what the fan is doing, often due to a breakdown in communication through the wiring. The fan gets stuck in a safety loop where it runs constantly because it isn't receiving the correct 'stop' signal from the control board. Most commonly, this is caused by aged electrical components or loose connections between the fan motor and the main circuit board.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.