The AC side of the water heater is independent of the propane side. It is the simplest to troubleshoot as well.
The two limit switches are located under the rubber reset covers. Press both (through the rubber cover!) and try the AC again.
If that does not work remove the two screws holding the rubber cover on and check for AC voltage. If you have voltage on one of the terminals of the AC limit switch but not on the other after you reset it, the limit switch is bad.
Note the one on the left (AC in this photo) has "opened" and the one on the right (DC) is "OK".
If you have AC voltage on both terminals and still no hot water, the heating element is bad.
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW