BoilerFaultCodesTechnical description
Return temperature is higher than the flow temperature. Insufficient water. No through flow. Too much air in the system. Sensors not wired correctly. Deviation in the flow or return temperature sensor.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the temperatures are the wrong way around or not changing as expected, suggesting water isn't moving through the unit. The most common reasons are a lack of water pressure, a buildup of trapped air pockets, or a pump that has seized and can no longer push water around your radiators. Essentially, the boiler is shutting down to prevent itself from overheating because the heat it produces has nowhere to go.
This issue often appears in autumn when the heating is turned on for the first time after summer, as pump components can seize during long periods of inactivity.
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.