BoilerFaultCodesTechnical description
Maximum water temperature: Rise in flow temperature too fast. Check: circulation pump; water flow through the unit; water pressure (0.8 bar min).
What causes this fault?
This fault occurs when the water temperature inside your boiler rises too quickly, causing the system to shut down for safety. The most common reasons are a pump that has failed to circulate water, a blockage in the pipework, or low water pressure, all of which prevent heat from being moved away from the burner. In some cases, air trapped in the system can also block the flow and trigger this overheat warning.
This fault is more common in autumn when heating systems are switched back on after being idle all summer, which can cause internal pump parts 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.