BoilerFaultCodesYour boiler has detected that its internal temperature sensors are reading back-to-front, which usually means water is flowing in the wrong direction or a sensor has failed.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Temperature differential inverted
What causes this fault?
This fault occurs when the boiler detects that the return pipe is becoming hotter than the flow pipe, which is the opposite of how the system should function. The most common reasons are a pump failure causing water to circulate backwards, a blockage in the heat exchanger, or one of the temperature sensors sending incorrect data to the control board.
This issue often surfaces when the heating is first turned on after summer, as internal pump components can seize up during long periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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