High Lockout
42E on Ravenheat HE 80/90 / 25-30s

Your boiler has shut down because there is a confusing difference between the temperatures recorded at its internal sensors, often caused by poor water flow or a sensors reading incorrectly.

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

Different temperature error

What causes this fault?

This fault occurs when the boiler's control system detects a significant conflict between the readings of the flow and return temperature sensors. The most common cause is poor water circulation through the heat exchanger, often due to a failing pump or debris in the system causing the water to overheat too quickly.

This issue often surfaces in autumn when the heating is turned on for the first time, as pump parts can seize or stick after being idle during the summer.

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

05EView →06EView →

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