BoilerFaultCodesWhat the manual says
Manufacturer manualpump / fan overrun
What causes this fault?
This occurs when the boiler has reached a high internal temperature and the pump or fan must continue running to dissipate that heat safely. The most common reasons are a blockage in the system restricting water flow, a pump that is beginning to fail, or a buildup of limescale inside the heat exchanger. Essentially, the boiler is struggling to push the hot water away from itself quickly enough after a cycle.
This issue is more frequent in summer when the central heating is rarely used, as pumps are more likely to seize or become sluggish after long periods of inactivity.
DIY fix possible
Check that at least one radiator is turned on fully (TRV set to max) to allow heat dissipationEnsure the system pressure is between 1.0 and 1.5 barWait up to 10 minutes for the boiler to complete its natural cooling cycleBleed radiators to ensure there is no trapped air affecting circulation
Avoid the next call-out bill
A cover plan would handle faults like S.15: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.