BoilerFaultCodesWhat the manual says
Manufacturer manualDHW mode: Fan overrun
From this model's manual
Verified against the Vaillant Ecotec Exclusive Combi installation & service manual, page 42.
What causes this fault?
This fault occurs when the boiler's central computer tries to start the fan but doesn't receive the required electronic pulse to confirm it is spinning at the right speed. It is usually caused by a physical blockage inside the fan's motor, a loose connection in the internal wiring, or a failure in the electronic components that monitor the fan's movement.
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.
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