Your boiler's computer has become stuck in a repeating internal test sequence and is failing to move into its normal heating mode.

Boiler operates with continuous relay test

What causes this fault?

This fault occurs when the boiler's internal electronic controller gets trapped in a perpetual diagnostic loop during its start-up sequence. It is typically caused by a hardware failure on the main circuit board where the internal switches fail to release or communicate correctly, preventing the system from ever reaching the ignition stage.