# How to decrease sensitivity to heat-bed temperature?

Sometimes I use a DIY 3D printer running Marlin firmware and I have a hard time to set my heat bed temperature. when I set it to 70 °C for PLA, after a few minutes it decreases to 67 °C and I see these error:

READ: Error:Thermal Runaway, system stopped! Heater_ID: bed


Since then the communication with printer is lost, the printing process stops and I have to reconnect to serial port... It's a disaster. I guess I need to lower the sensitivity to 3 degrees at least. I don't know how!?

• Have you PID tuned the heated bed?
– 0scar
May 7, 2019 at 10:58
• aside note: as an upgrade you can add an insulation under your HB to keep the temperature more constant May 7, 2019 at 11:32
• @0scar No, I'm using the default pid parameters. I Thought it would mess it up if I changed them. May 7, 2019 at 11:48
• @ darth pixel , I'm using an insulator, however it doesn't cover all the surface beneath HB. May 7, 2019 at 11:49
• First thing to do is do a PID tuning session! :)
– 0scar
May 7, 2019 at 11:57

I had a similar issue when printing with ABS, because my print cooling fan only activated once it got to a certain height above the bed. I'd say you need to do a PID tuning session, insulate the bottom of the bed better, and see if you can make sure your cooling fan doesn't blow air over the bed itself.

• Thank you. Since I did a pid tuning session everything is good. Jun 2, 2019 at 7:18

For people from google: Go to configuration_adv.h in the marlin firmware source code, and search for "THERMAL_PROTECTION_HYSTERESIS". Then increase the number. The number is how much degress celsius the temperature can be off before thermal runaway

• This is the correct answer to the question that was asked. While the solution to the OPs problem was pid tuning, this is the correct place in Marlin to change the number of degrees off before triggering an error. Sep 11 at 21:54
• @agarza this config changes the sensitivity of the thermal runaway. so its exactly what the op asked Sep 12 at 16:39
• Ok, I see now. This is basically a "how to fix it in code" solution. Learn something new everyday. Thanks for enlightening me. Sep 12 at 17:26