BoilerFaultCodesTechnical description
Maximum acceptable flow temperature rise exceeded. The boiler will shut off for ten minutes, then restart. Should the flow temperature conditions remain the same after 5 attempts, this code will be recorded as a shut-down failure. Boiler will not lockout.
What causes this fault?
This fault occurs when heat cannot be carried away from the boiler's heat exchanger quickly enough, leading to a rapid and unsafe rise in temperature. The most common reason is a failing internal pump or a blockage in the system pipework that restricts the flow of water. It can also be triggered by a build-up of limescale or sludge within the heat exchanger itself, which prevents efficient heat transfer.
This issue often surfaces during the first cold snap of autumn when the heating is turned on after a long summer break, as pumps can seize or sludge can settle while the system is inactive.
DIY fix possible
Check that all radiator valves are fully openEnsure the central heating bypass valve is openCheck that the boiler pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air