BoilerFaultCodesTechnical description
Water shortage, temperature spread between flow and return probe too large: Pump blocked or defective, pump output too low, flow and return sensor swapped over
What causes this fault?
This fault occurs when the water inside your boiler heats up much faster than it can be moved away into your radiators. The most common reason is a failing internal pump or a buildup of debris like sludge that is physically blocking the flow of water. When the boiler detects that the outgoing water is significantly hotter than the returning water, it shuts down to prevent the unit from overheating.
This issue is more frequent in autumn when the heating is first switched on after summer, as the pump can seize up after 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.