BoilerFaultCodesTechnical description
Temperature differential inverted (return sensor temperature higher than thermistors flowsensor temperature)
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the return pipe is hotter than the flow pipe, which is the opposite of how a heating system should function. The most common reasons are sensors that have shifted out of calibration, a faulty pump that isn't circulating water correctly, or a blockage in the heat exchanger.
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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