Vokera model, The Linea range- Linea 24?

Have a Vokera model, The Linea range- Linea 24 Linea 28 Boiler.
I have a problem with it, it keeps turning itself on so the heating and water are hot but the dial is at off and no display is showing and it stays on for about 20 minutes now, it has been happening once a day now and the booklet isn’t much help either. Using the gas as the flame on but the dial is on off.

Could you advice me on what could be wrong with it and how I go about mending it.
Any advice appreciated.