BoilerFaultCodesTechnical description
Heating mode – pump overrun error
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water isn't moving through the system quickly enough after the flames have gone out. The most common reasons are a failing circulation pump that can't push the water anymore, or a blockage caused by a build-up of sludge and debris in the pipework. Small mechanical parts like the check valve can also become stuck, physically preventing the water from flowing away from the heat exchanger.
This issue often surfaces in autumn when the heating is turned back on after a long summer break, as internal pump parts can seize up from lack of use.
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.