BoilerFaultCodesTechnical description
Actual temperature differential between flow and safety temperature sensor is too high
What causes this fault?
This fault occurs when water cannot move through the boiler fast enough to carry heat away, causing a rapid and dangerous rise in temperature. The most common reasons are a failed internal pump that has stopped spinning or a blockage caused by a buildup of sludge and debris within the main heat exchanger. In some cases, it may simply be caused by air trapped in the system or sensors that are providing incorrect temperature readings to the control board.
This fault often appears when the heating is first turned on after summer, as the internal pump 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.