BoilerFaultCodesTechnical description
Differential water flow switch is still open
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water isn't moving through the unit quickly enough to safely carry heat away. The most common reason is that the system pressure has dropped too low, but it can also be caused by a build-up of sludge or a large air bubble trapped inside the pump. In these cases, the boiler shuts down as a safety precaution to prevent the heat exchanger from overheating.
This fault is frequently seen in autumn when heating systems are turned back on after a long summer break, as pumps can seize or air pockets can settle during 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.