High Lockout
76 on Alpha E-Tec, E-Tec Plus, Evoke

Your boiler's internal thermometers are misreading the temperature or have failed, which has caused the system to shut down for safety.

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/flow sensor fault from possible failure of one or both sensors

What causes this fault?

This fault occurs when the boiler's control board detects that the temperature sensors (NTC thermistors) are sending conflicting information or no signal at all. The most common reason is a physical failure of the internal sensor probes, but it can also be caused by loose wiring or mineral buildup on the sensors preventing them from reading heat levels accurately.

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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