BoilerFaultCodesWhat the manual says
Manufacturer manualOutdoor Unit, Return Thermistor (Tw_In)
What causes this fault?
This fault occurs when the heat pump's control system loses the ability to accurately measure the temperature of the water returning from your radiators. This is usually caused by the internal electrical components of the sensor failing or the wiring becoming damaged, which prevents the unit from knowing how much heat is needed. Because the system can no longer safely monitor the heating cycle, it shuts down to prevent damage to the compressor.
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 9.1.12: no call-out fees, no surprise bills.
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