BoilerFaultCodesTechnical description
No water circulation, insufficient circulation or sensor error.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that heat is not being carried away from the burner quickly enough, leading to an overheat risk. The most common reasons are a failed pump that isn't pushing water around, or a blockage caused by sludge and debris inside the pipework or heat exchanger. In some cases, it may simply be caused by a faulty sensor sending an incorrect temperature reading to the main control board.
This issue often surfaces during the first cold snap of autumn when a pump that has been idle all summer fails to restart or struggles to move thickened sludge through the radiators.
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.