BoilerFaultCodesWhat the manual says
Manufacturer manualReturn heating thermistor fault
From this model's manual
Verified against the Glow Worm/Glow Worm Ultracom 35 Store 4701915 installation & service manual.
What causes this fault?
This fault occurs when the boiler's control board receives an incorrect or missing electrical signal from the sensor that monitors water temperature coming back from your radiators. The most common reason is that the sensor has physically failed due to age, though it can also be caused by loose or damaged internal wiring.
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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Related fault codes
All 70 fault codes on the Ultracom 35 Store
Seeing a different code? Every code this model can display, in one place.