BoilerFaultCodesYour boiler has detected that hot water is moving in the wrong direction or the temperature sensors have been confused, causing the system to shut down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Temperature sensor fault: a. Flow and return temperature sensors mixed up. b. Flow and return connections mixed up. c. Water flow in D.H.W.mode not correct.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that heat is flowing in the opposite direction than expected, often because the flow and return pipes are behaving incorrectly. The most common reasons are a blockage in the heat exchanger, a failing diverter valve that is sticking, or the temperature sensors themselves becoming faulty and giving the control board conflicting information.
This issue often comes to light in autumn when the central heating is turned back on after months of only providing hot water, putting stress on the diverter valve.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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