BoilerFaultCodesTechnical description
Central heating boil detected – boiler operating at minimum burner load with temperature difference greater than 18°C between Flow & Return.
What causes this fault?
This fault occurs when the water inside your boiler heats up too quickly because it isn't circulating around your radiators fast enough. The most common reasons are a failing internal pump that can no longer push the water, or a buildup of sludge and debris that has created a partial blockage in the main heat exchanger.
This fault often appears during the first cold snap of autumn when the heating is turned on after being dormant all summer, which can cause internal pump components to seize.
DIY fix possible
Check that all radiator valves (TRVs) are fully openEnsure the central heating system pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air