BoilerFaultCodesWhat the manual says
Manufacturer manualMixer closes - Heating circuit M2 flow temperature sensor shorted out
What causes this fault?
This fault occurs when the boiler loses connection with the sensor responsible for measuring the water temperature in your underfloor heating or radiator circuit. The most common reason is that the sensor's internal wiring has failed or short-circuited, meaning the boiler can no longer safely regulate the heat for that zone. Because the control unit doesn't know how hot the water is, it closes the mixing valve as a safety precaution to prevent overheating.
This fault often becomes apparent during the first cold spell of autumn when the heating is switched on after being idle all summer, putting strain on aging electronic sensors.
Engineer required
This fault requires 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 40: no call-out fees, no surprise bills.
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