BoilerFaultCodesWhat the manual says
Manufacturer manualControl mode, max. pump speed: Communication fault - variable speed heating circuit pump, heating circuit M2
What causes this fault?
This fault occurs when the boiler's main control board loses its digital connection with the internal pump, preventing the system from synchronising water flow with heat demand. The most common reason is a failure in the pump's internal electronic module or a loose connection in the low-voltage communication data cable. In some cases, a power surge or moisture ingress can damage the circuitry responsible for these signals.
This fault is frequently seen at the start of autumn when a pump that has remained stationary all summer is suddenly required to ramp up to full speed.
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.
Avoid the next call-out bill
A cover plan would handle faults like C6: no call-out fees, no surprise bills.
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