Your boiler has detected that water is not circulating correctly through the system before the heating process starts, causing it to shut down to prevent damage.

Pre-Circulation Fault

What causes this fault?

This fault occurs when the water inside your boiler heats up too quickly because it isn't moving through the system as it should. The most common reason is trapped air pockets that block the flow, but it can also be caused by a buildup of sludge or a failing pump that is struggling to push water around.