[JRTJH]

Three things to check:

1. The switch "hidden under the propane solenoid" (only on Suburban water heaters) is installed upside down, UP is off and DOWN is on...... If you have an Attwood water heater, you don't have this switch, but have an AC control module attached to the back of the water heater (under the bunk)

2. The two black rubber covers on the thermostat high limit switch locations may have a high limit switch under one or both, so with a finger, press the center of each black rubber cover. If there's a switch under it, you'll feel it "snap" as it re-engages.

3. The winterizing valve (that you found under the bunk) is the only valve on "current winterizing systems"... There is a one way valve at the top connection to the water heater (the hot water output) which prevents cold water from "backflowing" into the water heater.

The valve is a 1/4 turn valve. Pointing up, it flows through the cold water plumbing and connects to the hot water plumbing (winterization setting). Pointing down, it flows through the water heater and blocks the "bypass" tube (normal operation setting).

Chances are that you've either got the bypass set wrong and have heated the tank interior tripping the high limit switches

Or, you've got the electric element switch in the UP position, which is OFF. But that wouldn't explain why the propane setting isn't working. If (another potential) the electric element is working, once the water is hot, the propane side will not turn on until the water is used or cools below the thermostat setting (about 130-140*F)