@dc42 Thank you for the quick fix! Testing the new version right now. It appears to be functional but interestingly enough the PID values need to change slightly for it to function appropriately. Did something change in way those PID values are used?

@dc42 I sent you an email with the full configuration.

Something to note is if the bed heaters 2&3 are switched to chamber heaters this issue does not occur.

The M301's are in config-override:

; Heater model parameters
M307 H0 R0.356 C720.900:720.900 D1.10 S1.00 V24.2 B0 I0
M307 H2 R27.989 C33.988:33.988 D0.51 S0.80 V24.2 B0 I0
M307 H3 R3.786 C199.451:199.451 D4.01 S1.00 V24.1 B0 I0
M307 H4 R3.650 C231.039:231.039 D4.62 S1.00 V24.2 B0 I0
M307 H5 R0.486 C700.000:700.000 D10.00 S1.00 V0.0 B0 I0
M301 H5 P0.1 I9.000 D0.0
M307 H6 R0.486 C700.000:700.000 D10.00 S1.00 V0.0 B0 I0
M301 H6 P0.1 I9.000 D0.0

The mystery continues. Upon further investigation I have found that if I try running heater tuning (M303) the "bed heater" turns on and then rapidly turns back off.

The object model looks like this:

If I revert back to RepRap V3.3 everything works normally.

Here is the configuration in question:

; ---------------------- Closed Loop Flow control ----------------------
; Hot Air Pump
M308 S10 P"e5_temp" Y"linear-analog" A"HotPump" F1 B0 C100       ; Set Mass Flow Controller
M950 H5 C"!fan0" Q20000 T10                                      ; Configure pump as heater
M140 P1 H5                                                       ; Configure flow control as bed heater
M307 H5 B0                                                       ; Turn off bang-bang
M140 P1 S-273.15                                                 ; Ensure pump is off
M143 H5 S100 A1                                                  ; Set maximum flow rate
M570 H5 P5 T5 S0                                                 ; Set heater fault parameters to cancel print instantly

;Cold Air Pump
M308 S11 P"e6_temp" Y"linear-analog" A"ColdPump" F1 B0 C100      ; Set Mass Flow Controller
M950 H6 C"!fan1" Q20000 T11                                      ; Configure pump as heater
M140 P2 H6                                                       ; Configure flow control as bed heater
M307 H6 B0                                                       ; Turn off bang-bang
M140 P2 S-273.15                                                 ; Ensure pump is off
M143 H6 S100 A1                                                  ; Set maximum flow rate

After installing 3.4RC1 the issue with manual PID values on bed heaters 2&3 is back. This problem was fixed in 3.3beta7+3 or 4. Not sure where in the code the issue is coming from. The end state is that the bed heaters do not have correct PID values and will not turn on.

After installing V3.4beta7+1 I found that both of the manually entered PID values (M301) for "bed heaters" 2 and 3 (M140 P1 and P2) are not showing up in the object model. The "bed heaters" are configured with a linear analog closed loop feedback (M308 Y"linear-analong"). When switching from bed heaters to "chamber heater" this problem was alleviated.

No changes in configuration files between V3.3 and V3.4beta7+1 and working in V3.3.

I have also found the new heater autotune algorithm in 3.4beta7+1 to be more finnicky to tune hot air heaters than in V3.3. This may have to do with the very fast response time in heating air.