Geeetech

I have one of the first Acrylic I3 ProB printers and my hotend suddenly heats 35-40 degrees hotter that it's set for. I've changed thermistors twice (different types - both 100K ohms) with no joy. So I swapped boards thinking it was the firmware, but the the problem is still there. I can't set it lower than 175 or the extruder shuts off.Any ideas? Is there something in the firmware 'configuration h' file I could change to correct this?

Hi，Do you have a thermistor that tests the hot end?

Thank you William. Do you meant do I have a redundant means of checking the temp? No, but I can tell that it is too hot by the smell, looks of the print and the ease of which the filament can be pushed through the nozzle.
I checked the power supply, but it is outputting 12.12v, which is in the normal range. I did find a loose terminal, but tightening it didn't change things.

This is not a 'fix', but I changed the low limit 'safety' in the firmware to 140 instead of 170 so I could print, and what used to print at 205 is doing the same at 165 now. It seems stable, but I'd rather it tell the truth. I suspect that changing the thermal temperature sensor settings would possibly correct this but there are so many and I wouldn't know which one to use. It would just be trial and error.

It did go through a period of wild temperature swings before this occurred, but a change of the thermocouple would usually remedy it. Not this time.