thermal runaway on my hotend

I have recently built a prusa i3 clone (basically followed the youtube videos by Tom Sanladerer) and it was up and running and I printed a couple of prints with no issues, however after those first two prints, now I get a thermal runaway on the hotend and it kills the print after about 15 minutes of printing.

I have printing PLA and have had the hotend temp set at 200 degrees celcius. It is dropping to around 197 degrees when the print gets killed.

What could be causing this?

broken cable to heater cartage, check the cables

or another common issue the thirmistor is escaping from the heater block, just a very small gap can make it read low temp.

Quote
Dust
broken cable to heater cartage, check the cables

or another common issue the thirmistor is escaping from the heater block, just a very small gap can make it read low temp.

The cables to the heater don't seem to be broken. Is there another way to check if they are OK - such as with a multimeter?

I have just completed a pid autotune and when it finished it says to update the firmware with the pid values.

If I set the pid's in pronterface with the m301 gcode command, will that be a permanent change or do I still need to change the firmware via the configuration.h file?

Just sending it via pronterface is temporary

Unless you have eeprom enabled and save them with M500

NB after the first M500 command the values stored in eeprom take precedence of those in the firmware.

Or you could update your configuration.h

The PID autotune didn't seem to make a difference, and I have checked the heater cartridge wires which look fine. I replaced the thermistor just in case, and I'm still getting the issue.

It seems to happen when the print gets to a part where the extruder is going quicker than before...when it is printing a solid layer, and the temperature just seems to start dropping until the print is killed.

Are you fans setup correctly?

Should have one fan on the cooling find of the hotend, and another pointing at the past as its being printed.

Should not be any fans pointing at the heating block.

Hi Dust, the fans are installed correctly, however after a few more failed prints it does appear to be the part cooling fan that is also cooling down the hotend and causing the problem.

Is there a way to adjust the intensity of the part cooling fan?