Your boiler is confused because its internal thermometers are giving conflicting readings and don't agree on how hot the water actually is.

Flow/return temperature sensor permanent deviation

What causes this fault?

This fault occurs when the boiler's internal sensors provide temperature readings that are too far apart for the system to trust, suggesting the water is heating up in a way that doesn't make sense. The most common reason is that one of the sensors has developed a chemical or Electrical fault, but it can also happen if the sensors are incorrectly installed or have become loose from the internal pipework.