BoilerFaultCodesWhat the manual says
Manufacturer manualReturn thermistor fault
From this model's manual
Verified against the Ideal Logic System System installation & service manual, page 75.
What causes this fault?
This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water coming back from your heating system. The most common reason is that the sensor itself has suffered an internal electrical failure, though it can also be caused by loose wiring or a damp connection inside the boiler.
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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