BoilerFaultCodesTechnical description
Pump seized / Flow/return service valve closed
What causes this fault?
This fault occurs when the boiler detects that water is not circulating through the heat exchanger, triggering a safety shutdown to prevent overheating. The most common cause is the internal pump becoming seized or stuck, often due to a build-up of debris or the pump capacitor failing. It can also happen if the service valves underneath the boiler have been accidentally closed, physically blocking the path of the water.
This issue is particularly common in autumn when heating systems are turned back on after being idle all summer, as pumps often seize during long periods of inactivity.
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.