Webasto dual top winter boiler drain

Hi all,

Bought our first motorhome this year Autotrail Excel and with very cold weather forecast have followed handbook instructions to drain the boiler, webasto dual top system.

After completing the drain and putting the dial in the off position (control panel above the door) the whole control panel is flashing on and off. 

This isn't mentioned in the handbook not sure if this should happen or what else we need to do as no further instructions.

Any ideas please?