High Lockout
FU on Ideal Logic Max Plus

Your boiler has detected that water is heating up too quickly or not circulating properly, which usually means something is blocking the flow of water through 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

Diff greater than 50c check isolation valves are open

What causes this fault?

This fault occurs when the boiler detects a rapid rise in temperature because heated water isn't moving away from the burner fast enough. The most common reasons are a pump failure, a blockage in the pipework, or an internal part that has become restricted with sludge and debris.

This fault is more common in autumn when heating systems are first turned back on after the summer, as pumps can seize up during long periods of inactivity.

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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