High Lockout
H1 on Ideal Classic FF

Your boiler has detected that the water leaving the unit is getting too hot, causing it to shut down to prevent damage.

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 TEMPERATURE

What causes this fault?

This fault occurs when the water inside the boiler heats up too quickly or exceeds a safe temperature limit. The most common reasons are a pump failure that stops water from moving through the system, or a buildup of limescale and sludge that restricts flow within the heat exchanger.

This issue often surfaces during the first cold spell of autumn when the heating is turned back on after being idle all summer, which can cause internal pump parts to seize.

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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