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In the mornings my shop is cold, and it errors out my temperatures. so i have to pre-warm the hotend and bed with a heat gun before it will let me print. the led screen says "def" for both temps. it looks like it errors out at temps below 18*c. is there a way i can lower the temp it errors at so i can start prints in the cold?

It's probably better in the long run to pre-heat a bit as you've been doing rather than disable a safety feature.

g.

It could be worth at least looking to see what MIN_DEFECT_TEMPERATURE is in configuration.h. The default for 0.92.9 is -10, which shouldn't be problematic.

I've faced the same issue. I believe the setting is MIN_DEFECT_TEMPERATURE, which is set to 18. Note that the way we've adjusted the thermistor profiles, they are quite inaccurate at room temperature and below. I also agree with Geneb that disabling the feature, or reducing the sensitivity is a bad idea. I recommend that you build an enclosure with a separate temperature controller and some form of heater (reptile warmers, flat panel ceramic convection heaters, ETC, just not propane or something please), and leaving that running at a relatively low temperature overnight, and turning it up while actually printing. You'll have less trouble, and better quality prints.

If you install PEI, do not use a heatgun on it. I learned that the hard way, and now said PEI sheet was given away to be turned into a bed for a smaller printer. Instead, unclip the bed surface, and put your thumb over the thermistor location. Then once it stops erroring, get it to start pre-heating and up to ~50C before you put the build surface back. I also dis-recommend it for the hotend, due to the potential to warp the effector, ball joints, or tensioning springs.

So why would lowering the temperature it errors at, effect the temperature accuracy while printing? not sure i understand that??

It wouldn't affect anything while printing except it would reduce the instances when the protection would trigger. If the thermistor went to a dead short you'd still be fine but if the short had a resistance between the resistance that corresponds to your current setting and the resistance that corresponds to your alternate setting the protection would not trigger and you risk thermal runaway.

ah i get it, if the thermister broke and no current was going though it it would show a very low temp, that 18*c is just high enough that the thermister has to be working to go to that range in resistance. Do you think it is safe to just lower it a few degrees? what is the safety margin they used?

SeeMeCNC is usually pretty conservative with stuff that has the potential to affect safety. As I said, the default on the Repetier 0.92.9 configuration tool is -10. Personally I'd probably follow the advice to let it nudge you to a heated chamber. Printing in ambient temperatures below 18, you're going to have a lot of problems with warping, peeling up, and cracking.

so i just plugged in a completely open lead into the thermister slot, and it came back as 7* c so -10 would be pointless as a safty, so it looks like they put a safty margin of 11*c so i feel comfortable lowering it to 15* c.