Your boiler has detected that the water is not circulating correctly between the heating system and the boiler, which has caused it to shut down to prevent damage.

flow/return ∆T error

What causes this fault?

This fault occurs when the boiler's internal computer system experiences a temporary glitch in communication between its electronic components. It is most commonly caused by a minor electrical interference or a momentary loss of data signal, which prompts the boiler to automatically reset to ensure everything is working correctly.