I switched from out3 to out7 and mapped it per config file below and it works. I am not sure why but at least the chamber heater works now and I was able to tune it.
; Configuration file for Duet 3 (firmware version 3)
; executed by the firmware on start-up
;
; generated by RepRapFirmware Configuration Tool v3.1.4 on Thu Aug 13 2020 09:44:43 GMT-0700 (Pacific Daylight Time)
; General preferences
G90 ; send absolute coordinates...
M83 ; ...but relative extruder moves
M550 P"Duet 3" ; set printer name
M669 K1 ; select CoreXY mode
; Drives
M569 P0.0 S1 ; physical drive 0.0 goes forwards
M569 P0.1 S1 ; physical drive 0.1 goes forwards
M569 P0.2 S0 ; physical drive 0.2 goes backwards
M569 P0.3 S1 ; physical drive 0.3 goes forwards
M569 P0.4 S1 ; physical drive 0.4 goes forwards
M584 X0.0 Y0.1 Z0.2 E0.3:0.4 ; set drive mapping
M350 X16 Y16 Z16 E16:16 I1 ; configure microstepping with interpolation
M92 X160.00 Y160.00 Z640.00 E822.67:822.67 ; set steps per mm
M566 X600.00 Y600.00 Z300.00 E3600.00:3600.00 ; set maximum instantaneous speed changes (mm/min)
M203 X120000.00 Y120000.00 Z1200.00 E4800.00:4800.00 ; set maximum speeds (mm/min)
M201 X800.00 Y800.00 Z30.00 E80.00:80.00 ; set accelerations (mm/s^2)
M906 X1800 Y1800 Z3200 E1800:1800 I30 ; set motor currents (mA) and motor idle factor in per cent
M84 S20 ; Set idle timeout
; Axis Limits
M208 X0 Y0 Z0 S1 ; set axis minima
M208 X450 Y280 Z320 S0 ; set axis maxima
; Endstops
M574 X2 S1 P"io1.in" ; configure active-high endstop for high end on X via pin io1.in
M574 Y1 S1 P"!^io2.in" ; configure active-high endstop for low end on Y via pin !^io2.in
M574 Z1 S2 ; configure Z-probe endstop for low end on Z
; Z-Probe
M558 P5 C"^!io3.in" H2 F150 T1800 ; set Z probe type to switch and the dive height + speeds
M558 H2 ;*** Remove this line after delta calibration has been done and new delta parameters have been saved
G31 P1000 X0 Y0 Z0.722 ; set Z probe trigger value, offset and trigger height
M557 X0:450 Y20:280 S20 ; define mesh grid
; Heaters
M308 S0 P"temp0" Y"pt1000" R2200 ; configure sensor 0 as PT1000 on pin temp0
M950 H0 C"out0" T0 ; create bed heater output on out0 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 S170 ; set temperature limit for heater 0 to 170C
M308 S1 P"temp1" Y"pt1000" R2200 ; configure sensor 1 as PT1000 on pin temp1
M950 H1 C"out1" T1 ; create nozzle heater output on out1 and map it to sensor 1
M307 H1 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H1 S450 ; set temperature limit for heater 1 to 450C
M308 S2 P"temp2" Y"pt1000" R2200 ; configure sensor 1 as PT1000 on pin temp1
M950 H2 C"out2" T2 ; create nozzle heater output on out1 and map it to sensor 1
M307 H1 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H2 S450 ; set temperature limit for heater 2 to 450C
M308 S3 P"temp3" Y"pt1000" R2200 ; configure sensor 3 as PT1000 on pin temp3
M950 H3 C"out7" T3 ; create bed heater output on out7 and map it to sensor 3
M141 H3 ; Define heater h7 as chamber heater
M301 H3 P-1 ; Disable PID settings to use bang-bang
M143 H3 S150 ; set temperature limit for heater 3 to 150C
; Fans
; Tools
M563 P0 S"Mosquito Main 0" D0 H1 F0 ; define tool 0
G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets
G10 P0 R0 S0 ; set initial tool 0 active and standby temperatures to 0C
M563 P1 S"Mosquito Support 1" D1 H2 F0 ; define tool 1
G10 P1 X16.150 Y2.15 Z0 ; set tool 1 axis offsets
G10 P1 R0 S0 ; set initial tool 1 active and standby temperatures to 0C
; Custom settings are not defined
; Miscellaneous
M575 P1 S1 B57600 ; enable support for PanelDue
M501 ; enable config override
M572 D0 S0.7 ; enable pressure advance
