BoilerFaultCodesTechnical description
The heating return thermistor is too resistant.
What causes this fault?
This fault occurs when the internal control board receives a signal from the return water sensor that is outside of the expected range, suggesting the component is broken or disconnected. The most common reason is that the sensor's internal resistance has degraded over time, though it can also be caused by loose wiring or corrosion on the sensor pins. Because the boiler can no longer accurately monitor the temperature of the water coming back from your radiators, it shuts down to prevent overheating.
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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