dual Z motors, U "occasionally" goes crazy!?

[dc42]

Do you have a chamber heater configured? If so, check what happens if you disable it by never sending M141.

[andymidtf]

@dc42 No, there is no chamber heater configured... there IS a chamber heater, but it is completely independent (at the moment, I was thinking of later including control in the Duet), and is run by its own heater control.
I have M140 H-1 in config.g, so no instruction should be sent for bed/chamber anyway?

cheers!
andy