BoilerFaultCodesTechnical description
Over temperature on primary water circuit
What causes this fault?
This fault occurs when the water inside the boiler exceeds a safe temperature limit, causing the safety sensors to shut the system down. It is usually caused by a failure to move heat away from the burner, often due to a broken internal pump or a blockage in the pipework. In some cases, a build-up of limescale or sludge can restrict water flow, leading to rapid overheating.
This issue often surfaces during the first heavy use of the heating in autumn, as pumps can seize up after being inactive over the summer months.
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.
Find a Gas Safe engineer
Search the official register →