@droftarts Weird is that it is only happening during heatup, no issuse while printing.... no spikes during an 10 hrs printjob, then next heatup again spikes... maybe the firmware is poling the temp in different situations on different durations, so the spikes dont show during printing, maybe it polls more frequent during heatup... tried to wiggle the cables, but no drops or spikes...

and its an ATC Semitec 104GT-2 M3 screw-in sensor.
config-override:
M307 H0 R0.129 C700.000:700.000 D10.00 S1.00 V0.0 B1
M307 H1 R1.737 C336.747:336.747 D7.46 S0.75 V12.2 B0

Config:
; Heaters
M308 S0 P"bedtemp" Y"thermistor" T100000 B3950 ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0 ; create bed heater output on bedheat and map it to sensor 0
M307 H0 B0 S1.00 ; disable bang-bang mode for the bed heater and set PWM limit
M140 H0 ; map heated bed to heater 0
M143 H0 S120 ; set temperature limit for heater 0 to 120C
M308 S1 P"e0temp" Y"thermistor" T100000 B4725 C7.06e-8 ; configure sensor 1 as thermistor on pin e0temp
M950 H1 C"e0heat" T1 ; create nozzle heater output on e0heat and map it to sensor 1
M307 H1 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit

Here you can see the graph.

Hi
i used Duet for a long time, but since several firmwares i have a big issue while heating the extruder...
i often get a heater fault, checked wiring and Temp Sensor, no broken wires. In diagram it looks like
a wrong temp is read, there are temp spikes visible, also some time i got a temp rising too slow error...
Never had problems with firmware 2.x. It seems that some time the sensor is not read correctly.
And is there a way to set the expected rise delta somewhere?