High Lockout
Return Thermistor Fault on Ideal Logic Max System

Your boiler is struggling to monitor the temperature of the water returning from your radiators, which prevents it from heating your home or water efficiently.

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

Thermistor resistance value incorrect (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 sensor responsible for measuring the temperature of the water returning to the boiler begins to provide inaccurate readings or fails entirely. The most common reason is the internal electrical component within the sensor wearing out over time, though loose wiring or moisture on the connections can also disrupt the signal sent to the main control board.

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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