It looks to me like you have a 2 valve system. The bottom valve (at the T) should rotate (handle vertical) to bypass the water heater via the vertical pipe and the upper valve at the outlet (HOT) should be closed to winterize.
The upper valve should be open and the lower valve should be rotated so the handle is horizontal to allow cold water to enter the water heater so it can fill and get hot.
IF the water heater was in bypass and you turned on the AC power to the water heater, you could burn out the heating element in seconds and could need replacement. The high limit thermostat could also need to be reset.
Gas operation would also shut down due to the opening of the high limit thermostat. It is reset (after water is actually IN the heater
) by opening the outside metal panel and finding the rubber covered reset buttons and pressing gently. They should move inwards if the bellows is open.
It should also look like the "new" thermostat and not like any of the other photos of bad ones. The left on is the AC electric thermostat and the right one is for the gas system. THEY ARE NOT interchangeable.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW