BoilerFaultCodesTechnical description
Flow switch terminals are disconnected or flow switch is not activated
What causes this fault?
This fault occurs when the boiler's internal safety sensor cannot detect water circulating through the heat exchanger. The most common reason is a failed central heating pump or a blockage in the pipework that prevents the water from moving fast enough to trigger the flow switch. Without this movement, the boiler shuts down to prevent the internal components from overheating and sustaining damage.
This issue often surfaces in autumn when the heating is turned back on for the first time, as pump internal parts can seize up after being idle during the summer months.
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.