@Dennisdaan2 said in Duet 2 wifi heated bed heating when motherbord off:

M140 H0 S100 R80

Remove that entirely from your config.g

You've misunderstood how M140 works.

https://duet3d.dozuki.com/Wiki/Gcode?revisionid=HEAD#Section_M140_Set_Bed_Temperature_Fast_or_Configure_Bed_Heater

All you should have is M140 H0 that sets the H0 heater as a bed heater. Using S and R turns on the heater. The web interface isn't going to stop that. M140 S100 R80 will turn on the heater as soon as it's executed.