BoilerFaultCodesWhat the manual says
Manufacturer manualDHW mode – pump overrun error
What causes this fault?
This status occurs when the boiler is trying to move excess heat away from the internal heat exchanger after you have finished using hot water. It usually happens because the water isn't circulating quickly enough through the internal bypass or the pipes to cool the system down. The most common reasons are a pump that is starting to struggle or a slight internal blockage that restricts the flow of water.
DIY fix possible
Check that at least two radiator valves are fully open to allow water flowEnsure your boiler pressure is between 1.0 and 1.5 bar on the displayRestart the boiler to see if the status code clears
Avoid the next call-out bill
A cover plan would handle faults like S.17: no call-out fees, no surprise bills.
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Related fault codes
All 121 fault codes on the ecoTEC plus 624
Seeing a different code? Every code this model can display, in one place.