High Lockout
430 on Ideal Response SE

Your boiler has sensed that the temperature is rising too quickly or unevenly, which usually means water isn't flowing through the system as it should.

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

Maximum difference between T1 and T2 exceeded

What causes this fault?

This fault occurs when the heat generated by the burner cannot be carried away from the heat exchanger quickly enough, leading to a rapid heat spike. The most common reason is a failed circulation pump or a blockage in the system, such as sludge or debris, which prevents the water from moving. It can also be caused by a faulty sensor giving an incorrect temperature reading to the boiler's computer.

This issue often appears when the heating is first turned on after summer, as pump components can seize 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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