BoilerFaultCodesWhat the manual says
Manufacturer manualDHWmode:Pumpoverrun
What causes this fault?
This fault occurs when the boiler detects water flowing backwards through the internal system or senses an unusual pressure change when the pump starts. The most common reason is a blockage in the pipework or a failing non-return valve that is stuck open, allowing water to move in the wrong direction. It can also be triggered if the pump itself is struggling to circulate water effectively through the heat exchanger.
This issue often surfaces in autumn when the heating is turned on for the first time after summer, as internal valves can seize up during long periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Avoid the next call-out bill
A cover plan would handle faults like S.27: no call-out fees, no surprise bills.
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