@Phaedrux Ah, thanks. Your question helped me solve it. For some reason my printer manufacturer chose not to follow the recommendation in the Duet documentation whereby it is stated “our intention is that in a 3D printer with a single print head, you use the Fan0 output for the print cooling fan and the Fan1 output for the heatsink fan. This is the easiest configuration to use because it's what the firmware expects by default." Rather, they wired the part cooling fan up to Fan1 and the tool fan up to Fan0. In any case, I swapped them in the M950/M106 config commands and it works, now. The only thing that is mysterious to me is why it worked previously when I explicitly provided P0 in the M106 command.
