@gloomyandy i tried your suggested steps and here is the result :

Boot duet and sbc Turn on heater from dwc panel The fan don't turn on I turn off the heater wait for the temperature to go under 70°C hit emergency stop turn on heater fan don't turn on emergency stop (heater hot) fan turn on wait for the temperature to go under 70°C fan turn off Turn heater on Fan don't turn on

Here's the output of the M122 command :

=== Diagnostics === RepRapFirmware for Duet 3 MB6HC version 3.3 (2021-06-15 21:45:47) running on Duet 3 MB6HC v1.01 or later (SBC mode) Board ID: 08DJM-956L2-G43S8-6JTD6-3SS6K-KA1AH Used output buffers: 1 of 40 (14 max) === RTOS === Static ram: 150904 Dynamic ram: 62348 of which 0 recycled Never used RAM 140940, free system stack 202 words Tasks: SBC(ready,5.0%,330) HEAT(delaying,0.0%,325) Move(notifyWait,0.0%,302) CanReceiv(notifyWait,0.0%,908) CanSender(notifyWait,0.0%,374) CanClock(delaying,0.0%,339) TMC(notifyWait,7.1%,93) MAIN(running,87.7%,1250) IDLE(ready,0.1%,29), total 100.0% Owned mutexes: HTTP(MAIN) === Platform === Last reset 00:01:43 ago, cause: power up Last software reset at 2021-09-29 11:43, reason: StuckInSpinLoop, GCodes spinning, available RAM 143016, slot 2 Software reset code 0x4083 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0040080f BFAR 0x00000000 SP 0x2041970c Task IDLE Freestk 43 ok Stack: 00479e85 0047a862 61000000 a5a5a5a5 00479e85 a5a5a5a5 a5a5a5a5 2041ad9c 0000aaea 20432ac4 20424c74 20419728 20424c6c 00000004 2042cda0 2042cda0 20419728 00000000 00000001 20419784 4e49414d 00000000 00000000 00000001 00000001 00eec918 00000000 Error status: 0x00 Step timer max interval 154 MCU temperature: min 35.8, current 36.5, max 47.7 Supply voltage: min 24.3, current 24.4, max 24.4, under voltage events: 0, over voltage events: 0, power good: yes 12V rail voltage: min 12.0, current 12.0, max 12.0, under voltage events: 0 Heap OK, handles allocated/used 0/0, heap memory allocated/used/recyclable 0/0/0, gc cycles 0 Driver 0: position 0, standstill, reads 53339, writes 15 timeouts 0, SG min/max 0/0 Driver 1: position 0, standstill, reads 53339, writes 15 timeouts 0, SG min/max 0/0 Driver 2: position 0, standstill, reads 53339, writes 15 timeouts 0, SG min/max 0/0 Driver 3: position 0, standstill, reads 53340, writes 15 timeouts 0, SG min/max 0/0 Driver 4: position 0, standstill, reads 53340, writes 15 timeouts 0, SG min/max 0/0 Driver 5: position 0, standstill, reads 53341, writes 14 timeouts 0, SG min/max 0/0 Date/time: 2021-09-29 11:52:03 Slowest loop: 0.46ms; fastest: 0.04ms === Storage === Free file entries: 10 SD card 0 not detected, interface speed: 37.5MBytes/sec SD card longest read time 0.0ms, write time 0.0ms, max retries 0 === Move === DMs created 125, maxWait 0ms, bed compensation in use: none, comp offset 0.000 === MainDDARing === Scheduled moves 0, completed moves 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1 === AuxDDARing === Scheduled moves 0, completed moves 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1 === Heat === Bed heaters = 0 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1, chamberHeaters = 1 -1 -1 -1 === GCodes === Segments left: 0 Movement lock held by null HTTP* is doing "M122" in state(s) 0 Telnet is idle in state(s) 0 File is idle in state(s) 0 USB is idle in state(s) 0 Aux is idle in state(s) 0 Trigger* is idle in state(s) 0 Queue is idle in state(s) 0 LCD is idle in state(s) 0 SBC is idle in state(s) 0 Daemon is idle in state(s) 0 Aux2 is idle in state(s) 0 Autopause is idle in state(s) 0 Code queue is empty. === CAN === Messages queued 844, received 8, lost 0, longest wait 1ms for reply type 6018, peak Tx sync delay 607, free buffers 49 (min 48), ts 517/516/0 Tx timeouts 0,0,0,0,0,0 === SBC interface === State: 4, failed transfers: 1, checksum errors: 0 Last transfer: 1ms ago RX/TX seq numbers: 2731/2870 SPI underruns 0, overruns 0 Disconnects: 1, timeouts: 0, IAP RAM available 0x2c810 Buffer RX/TX: 0/0-0 === Duet Control Server === Duet Control Server v3.3.0 Code buffer space: 4096 Configured SPI speed: 8000000Hz Full transfers per second: 15.42, max wait times: 4.7ms/0.0ms Codes per second: 0.01 Maximum length of RX/TX data transfers: 3579/64

Extra temperature controlled exhaust fans.