BoilerFaultCodesGlow-worm Faulty CH thermistor Fault Code
Also written as FAULTYCHTHERMISTOR — same fault.
The Glow-worm Faulty CH thermistor fault code means: your boiler's internal thermometer is broken, meaning it cannot accurately tell how hot the water is and has stopped working as a safety precaution.. It appears on 1 Glow-worm model in our database.
Technical description: Resistance does not increase from approx 2.5K to 10K as boiler cools; replace.
What causes the Glow-worm Faulty CH thermistor fault?
This fault occurs when the internal sensor responsible for monitoring water temperature fails due to electrical degradation or internal corrosion. Over time, the sensitive components inside the thermistor can wear out or become coated in limescale, preventing the sensor from sending the correct electrical signal to the boiler's main control board.
This issue often becomes more apparent during autumn when the heating is turned on for the first time after summer, as the sensor struggles to cope with the sudden increase in thermal stress.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Glow-worm models that show the Faulty CH thermistor fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm Faulty CH thermistor fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026