High Lockout
L1 on Ideal Logic Combi C24 C30 C35

Your boiler has shut down because the water inside it has become too hot, usually due to a lack of circulation or a blockage in the system.

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

Flow Temp Overheat Lockout

What causes this fault?

This fault occurs when the internal sensors detect that the water is heating up too quickly or has reached a dangerously high temperature. The most common reason is that the water cannot move through the boiler properly, which is often caused by a failed pump, a blockage of sludge in the system, or air trapped within the unit.

This issue is more frequent during the first cold spell of autumn, when the heating is turned on after a long period of inactivity and the pump has seized up.

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 fault codes

L2View →F1View →

Related guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Radiators cold at the bottom

Sludge build-up — needs flushing, not bleeding.

Read →

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →