BoilerFaultCodes.com
F.71 High Lockout

Your boiler's internal thermometer is reporting a temperature that doesn't make sense, causing the system to shut down for safety.

Call an engineer soon

Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Fault: Flow sensor - Flow temperature sensor returns implausible values

What causes this fault?

This fault occurs when the boiler's internal computer receives conflicting information from the temperature sensor on the main pipe. The sensor may have developed an electrical failure, or it has become unclipped from the pipe, preventing it from accurately reading how hot the water is. To prevent the system from dangerously overheating, the boiler shuts down until the sensor is repaired or replaced.

Typical repair cost £100-220 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Protect yourself from future repair bills

A boiler cover plan would cover faults like F.71 — no call-out fees, no surprises.

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