Thermal Runaway I have been having problems with thermal runaways. It usually happens when the extruder is heating, but sometimes when the bed is heating. It happens usually during the first few minutes, but sometimes after a few hours. i have tried replacing the power supply. I also tried pid tuning. Anyone have any ideas what could cause this? Attached is a screenshot of a short print. https://reprap.org/forum/read.php?406,705690,705690#msg-705690 Wed, 09 Sep 2026 14:58:15 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?406,705690,710249#msg-710249 Re: Thermal Runaway https://reprap.org/forum/read.php?406,705690,710249#msg-710249
Quote
ianmcmill
This has been fixed but maybe others come here and have the same problem.

1.) Check that the thermistor is not cooled be any fan.
2.) Check that the thermistor is not damaged.
3.) Check in the firmware the timers for thermal runaway. Like tjnamtiw said: up the time. Default is 20sec. 30-40 sec is also fine.

In configuration.h, 'Residence time' is the time that the hot end has as a grace period to stay within a set range or get back there. Hysteresis is that range. In other words, if you set residence time to 10 seconds and hysteresis to 4 degrees, that means that when your temperature drops or rises more than 4 degrees from the set point, you have 10 seconds for it to get back into range. And once it is within range for 10 seconds, the computer will know it's OK to proceed.

I had this problem when my thermistor came partially out of the hot end and was being cooled by an A/C vent nearby. I also had the problem when the heated bed was situated directly under the hot end and the hot end fan was blowing on the heated bed thermistor area. That one was a head scratcher for a while.]]> tjnamtiw Prusa i3 and variants Tue, 27 Sep 2016 15:45:17 -0400 https://reprap.org/forum/read.php?406,705690,710227#msg-710227 Re: Thermal Runaway https://reprap.org/forum/read.php?406,705690,710227#msg-710227
1.) Check that the thermistor is not cooled be any fan.
2.) Check that the thermistor is not damaged.
3.) Check in the firmware the timers for thermal runaway. Like tjnamtiw said: up the time. Default is 20sec. 30-40 sec is also fine.]]> ianmcmill Prusa i3 and variants Tue, 27 Sep 2016 14:33:49 -0400 https://reprap.org/forum/read.php?406,705690,707332#msg-707332 Re: Thermal Runaway https://reprap.org/forum/read.php?406,705690,707332#msg-707332 fusa Prusa i3 and variants Wed, 14 Sep 2016 00:35:48 -0400 https://reprap.org/forum/read.php?406,705690,706607#msg-706607 Re: Thermal Runaway https://reprap.org/forum/read.php?406,705690,706607#msg-706607 tjnamtiw Prusa i3 and variants Sat, 10 Sep 2016 23:57:59 -0400 https://reprap.org/forum/read.php?406,705690,705706#msg-705706 Re: Thermal Runaway https://reprap.org/forum/read.php?406,705690,705706#msg-705706
Thanks for your reply.

I just took a temperature reading on the fuses using an infra red thermometer. They are 90-96F after printing for 4 hours.]]> fusa Prusa i3 and variants Wed, 07 Sep 2016 03:16:57 -0400 https://reprap.org/forum/read.php?406,705690,705703#msg-705703 Re: Thermal Runaway https://reprap.org/forum/read.php?406,705690,705703#msg-705703

They need to be cooled or they might overheat and cut power to bed or nozzle.
You might even want to replace them with standard blade fuses.
]]> Veesta Prusa i3 and variants Wed, 07 Sep 2016 02:23:33 -0400 https://reprap.org/forum/read.php?406,705690,705690#msg-705690 Thermal Runaway https://reprap.org/forum/read.php?406,705690,705690#msg-705690
Attached is a screenshot of a short print.]]> fusa Prusa i3 and variants Tue, 06 Sep 2016 22:15:29 -0400