Heated Bed Affecting Nozzle Temp Regulation

[carotti 0]

I have built a heated bed using 8mm aluminium plate. This is independently controlled and powered at the moment for simplicity. It sits at 110 degrees with not much variation as it is a huge thermal mass.

I have now noticed that it is seriously affecting the regulation of the nozzle temperature which was previously excellent.

This is resulting in serious ripple and layer separation in the z-axis when the temperature drops too low. (But with no warp!)

I am printing ABS at a set-point of 276 °C. The reported temperature from the thermocouple varies between 231 and 277 instead of the usual few degrees.

Marlin, Skein Py Py.

Can anyone offer any advice?

EDIT: I have eliminated a few variables (including the heated bed) and I think I have isolated the problem to the temperature control algorithm in Marlin. I will post my data in the Firmware, Marlin area as that seems to be the best place to find help for this problem