Your boiler has detected that the water inside is getting too hot too quickly, usually because there isn't enough water pressure or the water isn't moving through the pipes properly.

Flow temperature is higher than the set maximum temperature. Insufficient water. No through flow. Too much air in the system. Deviation in the flow or return temperature sensor.

What causes this fault?

This fault occurs when the heat inside the boiler cannot be carried away by the water quickly enough, causing the system to protect itself from damage. The most common reasons are a lack of water pressure, a blockage in the pipework, or a pump that has failed and stopped moving the water around. It can also happen if too much air is trapped in the boiler, creating an air pocket that stops the flow.