If you are certain that the red switch is NOT the gas water heater switch, then it is more than likely the tank heater switch, to keep your tanks from freezing. A lot of people run the gas AND electric at the same time on their water heater for speedy recovery. They are two separate systems. The electric side has an outside switch hidden behind the access cover. That must be on, as well as the water heater breaker in your converter service panel breakers for electric side operation. Gas turn on the illuminated rocker switch on the wall, and open the gas valve, and it will auto-ignite.
Hope this helps you! Randy
/SIGPIC]'08 V-lite Flagstaff 30WRLS
'06 Ram 1500 QC hemi
Reese dual cam sway control,
K&N series 77 intake, Hellwig helper spgs. LT tires,
Flowmaster "true duals", 380 h.p., Bilstein shocks