High Lockout
DHW Thermistor Fault on Ideal Logic Max Combi

Your boiler is struggling to accurately measure the temperature of your hot water, which typically means your taps will only run cold or have inconsistent heat.

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

Insecure electrical connection, incorrect resistance values (9.7-10.3 kΩ at 25°C), or lack of continuity between the PCB and the thermistor.

What causes this fault?

This fault occurs when the internal sensor responsible for monitoring hot water temperature starts sending incorrect signals to the main control board. The most common reason is that the sensor's internal components have degraded over time or a wire has shaken loose, leaving the boiler unable to tell how hot the water actually is. As a safety precaution, the boiler will stop heating the water to prevent it from reaching dangerous temperatures.

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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