BoilerFaultCodesTechnical description
Temperature differential inverted (return sensor temperature higher than flowsensor temperature)
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the water returning from your radiators is hotter than the water being sent out, which is physically impossible in a healthy system. The most common reason is a blockage or a pump failure preventing water from moving, though it is often caused by one of the temperature sensors simply failing and sending the wrong information to the control board.
This issue often surfaces in autumn when the heating is turned on for the first time after summer, as pump components can seize up 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.