Thermistors don't register a change in temperature.

I have a home-built Delta printer with a Melzi 2.0 motherboard from My problem is that the thermistor's aren't registering any temperature change when the board or hotend are heating up. Both will heat, but the thermistors still say 20 degrees. I've tried a few different thermistor tables (1, 96,97,98) but with the exception of #96 which had the thermistors registering room temperature at 36 degrees, no change. If the hotend or bed are heating up and I disconnect and then reconnect the printer to my computer, both thermistors will change to whatever the end or board are currently at, but they won't continue to change. Both thermistors read 133 ohms resistance at room temperature and both will show whatever temperature is being read, but they won't register any active change. What am I doing wrong?


  • Sounds more like you have disabled temperature reading in host. Printer Settings->Printer->Check Extruder and Bed Temperature.
  • Except I'm using Repetier firmware with Pronterface.
  • And I went and started Repetier host and that setting is checked in Printer Settings. It must be somewhere in the firmware
  • Just read "Both thermistors read 133 ohms resistance at room temperature". Thermistors have 100000 ohm at 25°C and resistance goes down with higher temperature. So I guess you have something different then the normap NTC thermistors, maybe thermocouples. But thermocouples need special hardware to be used and do not get connected to the thermistor sensors.
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