Your boiler is simply preparing to heat your home by getting the water moving before it ignites the burner.

Heatingmode:Pumppre-run

What causes this fault?

This fault occurs when the boiler detects that water is not circulating through the heat exchanger quickly enough to safely carry heat away. The most common reasons are a seized or failing internal pump, a blockage caused by sludge buildup, or air trapped within the pipework. Because the system cannot move the hot water out, it shuts down to prevent the internal components from overheating and sustaining damage.