@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.
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.