BoilerFaultCodesTechnical description
Pump modulation: Actual heating pump modulation.
What causes this fault?
This fault occurs when the boiler's control system detects that the internal pump is spinning at a different speed than required. The most common reasons are a buildup of debris or 'sludge' inside the pump that physically slows it down, or a communication failure between the pump and the main circuit board.
This issue often surfaces in autumn when the heating is turned back on after summer, as internal components can seize or become sluggish during long periods of inactivity.
DIY fix possible
Turn the boiler off at the fused spur switch for 30 seconds and turn it back on to reset the electronics.Check that all radiator valves are fully open to ensure water can flow freely.Listen for any unusual grinding or humming noises coming from the boiler casing.