Your boiler is currently running a self-diagnostic test or is in a temporary programming mode indicated by a yellow flashing light.

Led analysis test (blink yellow)

What causes this fault?

This code appears when the boiler’s control dial is moved into a specific position, triggering a self-test or setup mode. It usually happens if the dial has been accidentally moved past its normal settings or if the control knob is loose, causing the internal switch to sit between two functions. It is a temporary status rather than a mechanical failure of the internal components.