BoilerFaultCodesYour boiler's internal sensor that monitors the temperature of the water coming back into the unit has developed a fault, preventing the system from operating correctly.
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 stops receiving a reliable signal from the sensor that monitors the temperature of the water returning from your radiators. The most common reason is that the sensor itself has worn out or suffered an electrical failure, meaning it can no longer tell the boiler if it is safe to continue heating.
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 F5 — no call-out fees, no surprises.
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