BoilerFaultCodesYour boiler is struggling to monitor the temperature of the water returning from your radiators, which prevents it from heating your home or water efficiently.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Thermistor resistance value incorrect (9.7-10.3 kΩ at 25°C) or lack of continuity between the PCB and the thermistor.
What causes this fault?
This fault occurs when the sensor responsible for measuring the temperature of the water returning to the boiler begins to provide inaccurate readings or fails entirely. The most common reason is the internal electrical component within the sensor wearing out over time, though loose wiring or moisture on the connections can also disrupt the signal sent to the main control board.
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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