# Bed Thermistor Type Help
**URL:** https://marlin.crc.id.au/forum/t/bed-thermistor-type-help/856
**Category:** Firmware Builder
**Created:** [22 April 2022 21:06 UTC](https://marlin.crc.id.au/forum/t/bed-thermistor-type-help/856 "2022-04-22T21:06:13Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Kyle\_Hobbs](https://marlin.crc.id.au/forum/u/Kyle_Hobbs)
#### Post date: [22 April 2022 21:06 UTC](https://marlin.crc.id.au/forum/t/bed-thermistor-type-help/856/1 "2022-04-22T21:06:13Z")
Hi, I was looking to get the 410 x 410mm 1000W AC Heated Bed from 3Dfused to use on my 400xl Extended ender 3 Pro. It says it uses a " NTC 3950 thermistor" Does anyone know which thermistor this would be in the firmware builder? There arent any that match it exactly. Thanks in advance!
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### Author:  [@CRCinAU](https://marlin.crc.id.au/forum/u/CRCinAU)
#### Post date: [23 April 2022 03:29 UTC](https://marlin.crc.id.au/forum/t/bed-thermistor-type-help/856/2 "2022-04-23T03:29:41Z")
Try the generic 3950 ones - which are probably close enough - but you’ll likely have issues with overshoot on heatup etc…
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### Author:  [@Kyle\_Hobbs](https://marlin.crc.id.au/forum/u/Kyle_Hobbs)
#### Post date: [23 April 2022 12:43 UTC](https://marlin.crc.id.au/forum/t/bed-thermistor-type-help/856/3 "2022-04-23T12:43:29Z")
Is overshoot something that tuning the PID for the bed would help with?
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### Author:  [@CRCinAU](https://marlin.crc.id.au/forum/u/CRCinAU)
#### Post date: [23 April 2022 14:32 UTC](https://marlin.crc.id.au/forum/t/bed-thermistor-type-help/856/4 "2022-04-23T14:32:37Z")
To an extent… I have a 500W AC bed at 235x235 - and that overshoots as well… It’s only on the initial heatup, and it goes away and holds temperature well afterwards - but its not really critical.
I have a 70W hotend heater as well - which massively overshoots (by 10-15c) when using PID on the initial heatup. This screws up the filament and can make the first layer hit and miss to stick sometimes.
The new MPCTEMP feature in Marlin fixes this to the point where it overshoots a whole 0.5c. Eventually, I’m expecting that this is made available for the bed too - and our overshoot issues should be gone 🙂