BoilerFaultCodesTechnical description
waiting time: no water in system, temperature (gradient error) rise flow / return sensor too high
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the water temperature is rising far too quickly, which usually means the water is trapped and not flowing. The most common reasons are a failed circulation pump that can't move the water or a blockage caused by a build-up of sludge or air within the pipework. It acts as a safety measure to prevent the heat exchanger from overheating and sustaining permanent damage.
This fault often appears when the heating is first switched on after summer, as the internal 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.