BoilerFaultCodesWhat the manual says
Manufacturer manualDHW mode – fan overrun error
From this model's manual
Verified against the Vaillant Ecotec Pro Ecotec Plus System installation & service manual, page 59.
What causes this fault?
This fault occurs when the boiler’s software detects that the fan is still spinning at high speed after the demand for hot water has ended. The most common reason is a communication error between the fan and the control board, where the fan fails to slow down to a safe standby speed. It can also be caused by a sticking signal wire or a fault within the fan’s internal electronic motor.
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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