u/Huge-Chef-9262

I’m using an Octopus Pro v1.1 with a 3-wire PT100 and the onboard MAX31865. I changed the 0Ω resistor position for 3-wire mode according to the BTT manual and also changed the Marlin settings to TEMP_SENSOR_0 -5, MAX31865_SENSOR_OHMS_0 100, MAX31865_CALIBRATION_OHMS_0 430, and MAX31865_SENSOR_WIRES_0 3. The sensor reads temperature and the printer boots normally now, but the temperature reading seems very inaccurate. For example, when I set the hotend to 280°C, the display only shows around 250°C while the actual temperature appears to be well over 300°C based on filament burning behavior and external measurement. The PT100 measures about 109Ω at room temperature, so I think the sensor itself is probably okay. It’s a 3-wire PT100 with two red wires and one black wire. Measuring between the two red wires gives nearly 0Ω, and each red-to-black combination gives around 109Ω. I’m trying to figure out whether this is more likely caused by incorrect 3-wire wiring order, bad 0Ω resistor soldering, poor sensor contact with the heater block, or a damaged PT100/MAX31865 circuit. Has anyone seen similar behavior with the Octopus Pro onboard MAX31865?

I’m using an Octopus Pro v1.1 with a 3-wire PT100 and the onboard MAX31865. I changed the 0Ω resistor position for 3-wire mode according to the BTT manual and also changed the Marlin settings to TEMP_SENSOR_0 -5, MAX31865_SENSOR_OHMS_0 100, MAX31865_CALIBRATION_OHMS_0 430, and MAX31865_SENSOR_WIRES_0 3. The sensor reads temperature and the printer boots normally now, but the temperature reading seems very inaccurate. For example, when I set the hotend to 280°C, the display only shows around 250°C while the actual temperature appears to be well over 300°C based on filament burning behavior and external measurement. The PT100 measures about 109Ω at room temperature, so I think the sensor itself is probably okay. It’s a 3-wire PT100 with two red wires and one black wire. Measuring between the two red wires gives nearly 0Ω, and each red-to-black combination gives around 109Ω. I’m trying to figure out whether this is more likely caused by incorrect 3-wire wiring order, bad 0Ω resistor soldering, poor sensor contact with the heater block, or a damaged PT100/MAX31865 circuit. Has anyone seen similar behavior with the Octopus Pro onboard MAX31865?

Title: PT1000 + MAX31865 reading too low → heater overshooting (Octopus Pro v1.1)

Hi all, I’m troubleshooting a serious temp issue on my 3D printer and could use some help.

Setup

• Board: BTT Octopus Pro v1.1
• Sensor: PT1000 (3-wire)
• Interface: MAX31865 module
• Marlin firmware (configured for PT1000 + MAX31865)

Problem

• Display shows ~210–220°C
• But filament is clearly burning (actual temp seems way higher, ~300°C+)
• Eventually throws: “Heater failed system stopped heater E0”

What I tested

• Measured sensor at room temp → ~1000Ω (seems correct for PT1000)
• Boiling water test → only reads ~70°C (should be ~100°C)
• So it’s consistently reading too low

Current config

MAX31865_SENSOR_OHMS_0 1000
MAX31865_CALIBRATION_OHMS_0 4300

• Using 3-wire PT1000
• Firmware side looks correct (as far as I can tell)

My suspicion

• MAX31865 wiring or jumper configuration (2-wire vs 3-wire)
• Possibly wrong Rref on the module?
• Or incorrect 3-wire connection (same-color leads?)

Question

• What would cause a PT1000 + MAX31865 to read ~30% lower across the range?
• Could incorrect 3-wire jumper config alone cause this?
• Any quick way to verify correct wiring/config without damaging hardware?

Right now I’ve disconnected the heater for safety.

Any help would be really appreciated 🙏