BoilerFaultCodesYour boiler is unable to move water around the system because the pump is stuck or a valve has been accidentally closed.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Pump seized / Flow/return service valve closed
What causes this fault?
This fault occurs when the boiler detects that water isn't moving through the heat exchanger, often because the internal pump has physically seized after a period of inactivity. It can also be triggered if the service valves underneath the boiler have been accidentally turned off during DIY or maintenance, or if a build-up of sludge is blocking the internal flow. Without this circulation, the boiler shuts down to prevent the unit from overheating.
This issue is particularly common in autumn when homeowners turn their heating on for the first time after the summer, as the pump can stick if it hasn't moved for several months.
DIY fix possible
Check that the isolation valves underneath the boiler are in the open position (parallel to the pipework).Ensure all radiator valves are open to allow water to circulate.Try resetting the boiler to see if the pump clears its own blockage.
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