High Lockout
F5 on Ideal Logic+ Heat

Your 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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 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 is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F4View →F2View →L2View →

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