Your boiler is currently stuck in a diagnostic test mode that overrides its normal settings, which usually happens during a service or repair.

Set diverter valve position

What causes this fault?

This code appears because the boiler has been manually instructed to hold its internal diverter valve in a specific position for testing purposes. This usually happens during a professional service when a technician needs to isolate the heating or hot water circuits to check for leaks or performance issues. If the code remains on the screen, the boiler has simply not been exited out of this specific diagnostic menu.