High Lockout
24 on Intergas Combi Compact HRE 36/30

Your boiler has sensed that the water returning from your radiators is hotter than the water leaving the boiler, which usually means there is a circulation problem or a sensor fault.

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 sensor temperature > flow sensor temperature.

What causes this fault?

This fault occurs when the boiler's internal sensors detect that the system is operating in reverse, with the return pipe being hotter than the flow pipe. The most common reason is a circulation failure, often caused by a faulty pump or a blockage in the heat exchanger that prevents water from moving through the boiler correctly. It can also be triggered if one of the temperature sensors has failed and is providing an incorrect reading to the control board.

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.

Find a Gas Safe engineer
Search the official register →

Related guides you might find useful

Radiators cold at the bottom

Sludge build-up — needs flushing, not bleeding.

Read →

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →