BoilerFaultCodesTechnical description
Different temperature error
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water isn't moving through the system correctly, leading to a sharp temperature gap between the flow and return pipes. The most common reasons are a failing circulation pump that can't push water around or a blockage in the heat exchanger caused by a buildup of limescale or sludge. In some cases, it may simply be a faulty sensor providing an incorrect temperature reading to the main control board.
This issue often surfaces in autumn when the heating is turned back on after a long summer break, as pump components can seize up from lack of use.
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.