Technical description
Problem with the pump circulation
What causes this fault?
This fault occurs when the water inside the boiler gets too hot because it isn't being moved away quickly enough to the radiators. The most common reason is a failing internal pump that has stopped spinning, or a blockage of debris and sludge that is restricting the flow of water. It can also be caused by air trapped inside the unit which prevents the pump from working effectively.
This fault is frequently seen in autumn when the heating is turned back on for the first time after summer, as the pump can seize up 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.