Your model/vintage of water heater uses 2 separate sets of t-stats for electric and propane
Electric has it's own set on backside of water heater where the electric element is
Propane has it's own 12V DC set in outside compartment (ECO----high temp t-stat and T-stat----normal temp t-stat)
Brown wire comes from circuit board to/thru a 'thermal fuse' (one shot fuse inside clear tubing) to & thru normal t-stat and back to circuit board
Red wire comes form circuit board to & thru ECO then to gas valve
If 'thermal fuse' has blown......no DC so no propane function
It normal t-stat has failed or bad terminal/contacts...no DC so no propane function
If ECO t-stat has failed or bad terminal/contacts.....no DC so no propane function
With propane On/Off switch on......check for 12V DC on Brown & Red wires.
Trace where you loose it
If thermal fuse has blown..........need to clean burner/combustion chamber
Thermal fuse blows at 190*F due to blow back of propane flame due to obstruction/blockage in combustion chamber/burner
