BoilerFaultCodesYour boiler has lost its ability to monitor the temperature of the water returning from your radiators, often causing it to shut down to prevent damage.
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 sensor responsible for measuring the temperature of the water entering the boiler from your heating system fails or sends an incorrect signal. The most common reason is that the internal component has simply worn out over time, though it can also be triggered by loose electrical connections or moisture damage to the sensor. To protect the boiler from overheating, the system stops firing because it can no longer safely monitor the internal water temperature.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like F5 — 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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