Technical description
Reset the boiler – no circulation, sensor fault either not connected or has a bad connection.
What causes this fault?
This fault occurs when the boiler's internal computer detects that water isn't flowing through the heat exchanger, or it loses contact with the sensors that monitor temperature. The most common reason is a failed circulation pump that can no longer move water around your radiators, or a loose electrical connection between the sensors and the main control board.
This issue is more frequent in autumn when heating systems are turned back on after a summer of inactivity, which can cause the internal pump to seize.
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.