Heater Temperature Excursion



  • Started getting spontaneous heater faults recently, and I can't understand what's going on. Hoping the good folks here can share some troubleshooting tips.

    Error text for easier search engine indexing for future trouble shooters:

    Error: Heater 1 fault: temperature excursion exceeded 15.0°C (target 240.0°C, actual 268.9°C)
    Resume state saved
    Warning: Tool 0 was not driven because its heater temperatures were not high enough or it has a heater fault

    One of the times it happened:
    bec37ce1-6951-4613-8345-720916a1768a-image.png

    What I tried:

    • Heating to 240c, and jiggling all the wires on the hotend (thermistor + heater) - no change
    • Printing same file multiple times - fault at different layers
    • Anecdotal: I saw some noise on the bed heater a few days ago, which seemed to go away by itself. noise on that sensor also makes no sense since it's a very large bed with lots of thermal mass. it went away and didn't come back.

    The fact that I couldn't reproduce by moving the wires around makes me feel like this might be a noise/EMI issue? but why would it suddenly appear? why would it happen after several layers (which are basically identical)?
    Any tips on where to look next?



  • Had similar issue. Could not reproduce it by moving wires (at the beginning) but it was a broken heatbed thermistor wire (in Your case hotend thermistor wire). It started as a "noise" on temperature reading and finished with open circuit in about 2 weeks.



  • I tried reproducing by extruding material, and was inexplicably able to reproduce the bed heater noise flickering:
    098d6d32-2dc3-41dc-8a36-10e1578935f8-image.png

    @BoA The fact that it's happening on two different thermistors "at the same time" is suspicious to me (i.e. less likely to be a thermistor fault), don't you think?


  • Moderator

    How is your wiring for the thermistors ran?

    The graph in your first photo is clearly signal noise. It thinks the temp is dropping and increases power to maintain temp, but then it gets a real reading and sees the temp is actually hotter than expected and triggers the fault.

    I would be inclined to replace the thermistor and wiring entirely.



  • @Phaedrux said in Heater Temperature Excursion:

    How is your wiring for the thermistors ran?

    The graph in your first photo is clearly signal noise. It thinks the temp is dropping and increases power to maintain temp, but then it gets a real reading and sees the temp is actually hotter than expected and triggers the fault.

    I would be inclined to replace the thermistor and wiring entirely.

    Thanks for the tip @Phaedrux, in my delta I have 3 wiring harnesses (one in each tower) and the hotend thermistor was running along side the hot end fan for a long distance.

    I moved the fan to a different harness and was able to print without errors again, though the noise was significantly higher in the bed thermistor for some reason. (does not go through that harness at all).

    I can't really understand why this issue suddenly popped up, and I can't say that I feel like I solved it since the temperature readings for the bed were so noisy in the beginning (but became completely smooth after the bed was up to temp).

    Is there perhaps a way to filter transients in the temperature probe? (I meam physically, like a ferrite or a capacitor)


  • Moderator

    @Leav said in Heater Temperature Excursion:

    Is there perhaps a way to filter transients in the temperature probe? (I meam physically, like a ferrite or a capacitor)

    Not sure about that.

    Twisted pair and/or shielded cable can help avoid picking up noise. A PT100 in 4 wire mode is a good choice in this situation as it is designed to reject noise.



  • @Leav For heatbed this looks like a noise, but honestly... 50*C drop for about 60 seconds? That is not a noise. That looks like poor connection to heater.


  • Moderator

    @BoA said in Heater Temperature Excursion:

    That looks like poor connection to heater.

    If it was actually losing connection it would show open circuit and temp would shoot to 2000c to trigger fault.



  • @Phaedrux It would show open circuit in case of problem with thermistor, but on second pic it looks like bad connection to heater.


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