High Lockout
436 on Ideal Ideal Classic SE15P FF

Your boiler has stopped working because one of its internal temperature sensors has broken or become disconnected.

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

NTC1 open

What causes this fault?

This fault occurs when the boiler's control system can no longer read the temperature from the flow sensor, which acts like a thermometer for the water leaving the unit. The most common reason is that the sensor's internal electrical circuit has failed or a connecting wire has come loose, meaning the boiler shuts down for safety because it cannot monitor if it is overheating.

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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