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