# Can you not use a custom thermistor for a temperature\_fan?

**URL:** <https://klipper.discourse.group/t/can-you-not-use-a-custom-thermistor-for-a-temperature-fan/3929>\
**Category:** General Discussion\
**Created:** [August 23, 2022, 2:16am UTC](https://klipper.discourse.group/t/can-you-not-use-a-custom-thermistor-for-a-temperature-fan/3929 "2022-08-23T02:16:32Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Akanar](https://avatars.discourse-cdn.com/v4/letter/a/4491bb/32.png) [@Akanar](https://klipper.discourse.group/u/Akanar)\
**Post date:** [August 23, 2022, 2:16am UTC](https://klipper.discourse.group/t/can-you-not-use-a-custom-thermistor-for-a-temperature-fan/3929/1 "2022-08-23T02:16:32Z")

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I get `Unknown temperature sensor 'CMFB103F3950FANT'` for the following config.

```auto
[temperature_fan exhaust_fan]
pin: PD14
sensor_type: CMFB103F3950FANT
sensor_pin: PF5
min_temp: 0
max_temp: 100
control: watermark

[thermistor CMFB103F3950FANT]
temperature1: 0.0
resistance1: 32116.0
temperature2: 40.0
resistance2: 5309.0
temperature3: 80.0
resistance3: 1228.0

```

But I can use it just as a temp sensor without error.

```auto
[temperature_sensor chamber]
## Chamber Temperature - T1
sensor_type: CMFB103F3950FANT
sensor_pin: PF5
min_temp: 0
max_temp: 100
gcode_id: chamber_th

```

I obviously comment out that when I try to use temperature\_fan so I am not using the pin twice.  
[https://www.klipper3d.org/Config\_Reference.html#thermistor](https://www.klipper3d.org/Config_Reference.html#thermistor)

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**Author:** ![jakep\_82](https://avatars.discourse-cdn.com/v4/letter/j/ea666f/32.png) [@jakep\_82](https://klipper.discourse.group/u/jakep_82)\
**Post date:** [August 23, 2022, 4:43am UTC](https://klipper.discourse.group/t/can-you-not-use-a-custom-thermistor-for-a-temperature-fan/3929/2 "2022-08-23T04:43:24Z")

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The order of definitions in the config is important. You need to define the thermistor before you use it elsewhere in the config. Simply moving the thermistor above the temperature\_fan should fix it.

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**Author:** ![Akanar](https://avatars.discourse-cdn.com/v4/letter/a/4491bb/32.png) [@Akanar](https://klipper.discourse.group/u/Akanar)\
**Post date:** [August 23, 2022, 8:20am UTC](https://klipper.discourse.group/t/can-you-not-use-a-custom-thermistor-for-a-temperature-fan/3929/3 "2022-08-23T08:20:16Z")

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That did the trick. Documentation should probably remind users of this in the custom thermistor section.

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**Author:** ![ReXT3D](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/rext3d/32/200_2.png) [@ReXT3D](https://klipper.discourse.group/u/ReXT3D)\
**Post date:** [August 23, 2022, 12:50pm UTC](https://klipper.discourse.group/t/can-you-not-use-a-custom-thermistor-for-a-temperature-fan/3929/4 "2022-08-23T12:50:24Z")

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It’s already there:

“Be sure to place the thermistor section in the config file above its first use in a heater section.”

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<div class="post-metadata">

**Author:** ![Akanar](https://avatars.discourse-cdn.com/v4/letter/a/4491bb/32.png) [@Akanar](https://klipper.discourse.group/u/Akanar)\
**Post date:** [August 23, 2022, 5:14pm UTC](https://klipper.discourse.group/t/can-you-not-use-a-custom-thermistor-for-a-temperature-fan/3929/5 "2022-08-23T17:14:03Z")

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Ah, I see my thought process. It says “heater section” and I am using it in the fan section and I didn’t put two and two together. Then I guess it should be changed to something like…

“Be sure to place the thermistor section in the config file above its first reference as a sensor type or it won’t be recognized as a known sensor.”

… for idiots like myself. 🙃

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**Author:** ![EddyMI3D](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/eddymi3d/32/1981_2.png) [@EddyMI3D](https://klipper.discourse.group/u/EddyMI3D)\
**Post date:** [July 6, 2024, 5:46am UTC](https://klipper.discourse.group/t/can-you-not-use-a-custom-thermistor-for-a-temperature-fan/3929/6 "2024-07-06T05:46:07Z")

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