M143 H1 S320 sets the max temperature to 320

I added this to config.g just before the extruder PID section and it seems to work

When I run M303 H1 S320 it completed successfully, I added it's suggested PID values to config.g

The next print came out perfect, and there we no heater faults.

So the answer in this case is add M143 H1 S320 to the config.g file and auto-tune the heater with M303 H1 S320.

https://duet3d.dozuki.com/Wiki/Gcode#Section_M109_Set_Extruder_Temperature_and_Wait