This fault indicates that the flame induction gas valve cannot be started before ignition.

Generally, it depends on the style of your wall-hung boiler.

If it is model 2000 or model 3000, the ion bar can be removed and cleaned.

If it is a famous product, the photocell is broken. The way to judge its quality is to unplug it and start the wall-hung boiler. If it is lit, it will go out. 0 1 is that it has a problem. If it is still 02, there is something wrong with the main controller.