BoilerFaultCodesTechnical description
Differential temperature adjustable from 0 to 40K
What causes this fault?
This fault happens when the difference in temperature between the water leaving the boiler and the water returning to it exceeds the limit you have manually set in the settings. It usually occurs because water isn't moving through the system at the expected speed, often due to a pump working too slowly or a slight blockage in the pipes. In some cases, it simply means the monitoring sensors are giving slightly inaccurate readings and need to be recalibrated.
This code is more common when the heating is first turned on in autumn, as pumps can seize after being idle all summer or air trapped in the radiators can restrict the flow of water.
DIY fix possible
Check that all radiator valves are fully openEnsure the central heating system pressure is between 1.0 and 1.5 barBleed any air from radiators to ensure smooth water flow