BoilerFaultCodesYour boiler is staying in a cooling-down phase for longer than expected because it is trying to move excess heat away from the internal components.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: pump / 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 all radiator valves are fully open to allow water to circulateEnsure the system pressure is between 1.0 and 1.5 barSwitch the boiler off and on again to see if the status clears
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like S.15 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Glow-worm Flexicom cx is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.