BoilerFaultCodesTechnical description
Max.water temperature: Return temperature too high.
What causes this fault?
This fault occurs when the water coming back into the boiler is nearly as hot as the water going out, suggesting the heat has nowhere to go. The most common reasons are a pump failure that isn't moving the water around your house, or a blockage such as closed radiator valves or a clogged heat exchanger. It can also be caused by a faulty sensor that is incorrectly reporting the water temperature to the control board.
This issue often surfaces during the first cold spell of autumn when heating systems are turned back on after a long summer break, which can cause internal pump components to seize.
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.