BoilerFaultCodesTechnical 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.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.