Cold weather (-20c ; -4F) crash - fan 100% and lost EEPROM info


Louis P

New member

I was doing a low and slow cook yesterday at 225 when after about 4 hours, the HM (not the Pi) crashed and the fan went 100%. I realized it when the pit temp got to about 500F. The ribs were still edible, but my issue is that while that happened, it looks like the atmega lost all EEPROM parameters (probe names, custom PID values, custom probe coefficients, etc.)

I'm trying to understand 2 things. First, how did this happen? I looked at the list of parts (4.3) and most are more than ok at -20C except one: the resonator, which has a minimal operating temperature of -20. I'd assume some form of safety factor here, but the temperature in which the HM was operating was indeed -20C. So I could see that with a resonator starting to get funny, the atmega could crash.

The second thing I'm trying to see is if there's any way I could recuperate the previous values of the EEPROM, especially the PID values, which were painstakingly tweaked. The probes I don't care so much as Bryan made an excellent tutorial on how to do this when a standard probe is known and trying to calibrate an unknown probe. I'm very familiar with command line stuff; I looked around a bit but couldn't find anything other than a file called "autobackup.rrd" but it's binary and couldn't figure how to read it.


Bryan Mayland

TVWBB Hall of Fame
Wow that's certainly interesting, I've never heard a report of something like this happening before. I've also never done any cold weather testing because it never gets very cold here in Tampa. You'd think everything would be warmed up by the electronics to stay well away from the -20C operating limit.

The bad news is that on boot if the EEPROM doesn't have the right magic in it, it is assumed to be a fresh install so the entire block is initialized with the default values so there's no recovering what was there before. The autobackup.rrd is the history database and does not contain any configuration information either.

If you've used an Archive operation (stashing the database) then that does make a backup of the configuration at that time. It isn't shown on the webui, but the configuration is stored in `/mnt/mmcblk0p4/stash` as a json file with the same name as the RRD stash file. If you've never done an Archive operation then I can't think of anywhere else you'd be able to find the old config.


TVWBB Wizard
I'd suggest that I can do some cold weather testing (I expect 1-2 weeks of -10 to -20 F,) but for all appearances, it'll have to wait for a year. FWIW, I have never had an issue with the cold, and I've used it at -6 F. Problem with that is that I built a pocket in my smoker for it and it gets a little heat from the firebox. No issues with either heat or cold at this point.

J Halvo

TVWBB Member
I've used mine in Minnesota winter without issues. The LCD doesn't like the move too quickly but nothing has died to date.


TVWBB Member
that's really unfortunate! I did a brisket over the weekend, I went out at 2AM to pull & wrap, it was -9°F in the open with a nasty wind. No electronics issues, other than the opening of the blower almost froze over INSIDE the Egg!!! I'll have to go easy on the water in the drip pan next time I guess lol. Also had a rough time with the temp at the beginning, it was so windy, it kept blowing down the chimney and fueled the fire so much the temp took off & I had to shut it down to almost flame out & start over.


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