SOLVED Bed heater problem.

  • Just finished a new build 400x400x500 with a brand new duet wifi and there seems to be a problem with the bed heater. I am using a silicon bed heater switched with a SCR.
    The bed temperature is showing 2000 which indicates a thermistor problem. When I swap the bed thermistor with the hot end thermistor the hot end reads room temp and bed still shows 2000C.
    I am using the same configuration as my previous build which also uses a duet wifi.

    Is there any other reason the bed temp would read 2000C apart from a faulty board?


  • If you are swapping those thermistors at the board connection, yes. OR... Your plugging the "bed" thermistor in the wrong place (and / or the config has changed the place).

    But, yeah, if it is plugged in the right place, and swapped thermistors work via other inputs... then 😞

    My heater section looks like this:

    ; Heaters
    M305 P0 T100000 B4138 C0 R4700		; Bed. Set thermistor + ADC parameters for heater 0
    M143 H0 S100				; Bed, Set temperature limit for heater 0 to 120C
    M305 P1 T100000 B4138 C0 R4700 H-10   ; Hot End. Set thermistor + ADC parameters for heater 1.   H is offset correction at High resistance (low temps). DE 2018 01 28
    M143 H1 S280                          ; Hot End. Set temperature limit for heater 1 to 280C

    And my bed thermistor is plugged in like this (yellow wires):

    0_1547850364242_IMG_0134 (1)_LI.jpg

  • Thanks Danal,

    Yes I have an Identical set up apart from having the semicondutor relay connected in place of the bed heater so its looking like a board problem.
    I have just removed the board and there is no visual sign of any damage. I could swap it with my other machine but dont think it will prove anything more.

    I will contact the suppliers on Monday and see what they say.



  • I have just found an extra M307 H0 line in my config.g. It was hiding in the stepper settings.
    I have removed it and the bed heater is now working.

    I dont know where it came from but I cant blame anyone but myself.


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