BoilerFaultCodesTechnical description
Differential water flow switch fault (still closed).
What causes this fault?
This fault occurs when a mechanical sensor inside the boiler is stuck in the 'on' position, incorrectly signaling that water is flowing through the system. This is usually caused by a buildup of debris or sludge from the heating system jamming the moving parts, or a faulty pump that isn't shutting down correctly. Because the boiler thinks water is moving when it shouldn't be, it shuts down as a safety precaution to prevent damage.
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 →