BoilerFaultCodesTechnical description
(837/637 only) | Main heat exchanger anti freeze protection mode due to fan speed deviation too great | Check fan control cables/connections; Defective fan control cable;
What causes this fault?
This fault occurs when the boiler's computer detects that the fan is not spinning at the required speed to safely extract exhaust gases. The most common reason is a mechanical failure within the fan motor itself, though it can also be caused by loose wiring or a communication error from the main control board. If the fan cannot clear the fumes effectively, the boiler will shut down as a built-in safety precaution.
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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