BoilerFaultCodesYour boiler has detected a problem with the sensor that monitors the temperature of the water returning to the unit, causing it to shut down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Return Thermistor Fault
What causes this fault?
This fault occurs when the boiler's internal computer receives an unlikely or out-of-range signal from the sensor that monitors water coming back from your radiators. The most common reason is that the sensor has physically failed or developed a loose connection, meaning the boiler can no longer safely regulate its temperature.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like L5 — no call-out fees, no surprises.
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