BoilerFaultCodesTechnical description
The heating flow thermistor is detecting a temperature in excess of 100°C.
What causes this fault?
This fault occurs when the water leaving the boiler reaches a dangerously high temperature, causing the system to shut down to prevent damage. The most common reasons are a pump failure that prevents water from moving through the system or a build-up of sludge and debris that blocks the main heat exchanger. It can also be caused by a faulty sensor that is incorrectly reporting the temperature to the control board.
This issue is more frequent during the first cold spell of autumn when the pump may struggle to start after being idle throughout 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.