BoilerFaultCodesYour boiler has detected an issue with a temperature sensor that monitors the water returning from your radiators, preventing the system from heating up safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Wiring or resistance issues with the Return Thermistor located in the pump housing (upper LHS of boiler).
What causes this fault?
This fault occurs when the boiler's control board receives an incorrect or missing signal from the sensor that measures the temperature of the water coming back from your radiators. The most common reason is that the internal sensor has developed a physical defect or the electrical connection has become loose or corroded over time.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like Return Thermistor Fault — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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