BoilerFaultCodesTechnical description
Fault: Flue non-ret. valve/condens. pump - No flue non-return flap feedback; condensate pump overflow
What causes this fault?
This fault happens when waste water from the combustion process cannot escape because the condensate pump has failed or the drainage pipes are blocked. It can also be triggered if the safety flap in the exhaust flue is stuck, which prevents the boiler from safely venting gases. When the system detects that water is backing up or air cannot flow correctly, it shuts down to prevent internal flooding or safety issues.
This fault is more common during freezing winter temperatures, as the external pipe that carries waste water away can freeze solid and cause a backup into the pump.
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.