BoilerFaultCodesTechnical 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 is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.