BoilerFaultCodesWhat the manual says
Manufacturer manualReturn Thermistor Fault
What causes this fault?
This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water returning from your radiators. The most common reason is that the sensor itself has developed an electrical fault or has become corroded over time, though it can also be triggered by loose or damaged internal wiring. Because the boiler can no longer accurately track water temperature, it shuts down as a safety precaution to prevent overheating.
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 L5: no call-out fees, no surprise bills.
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