Re: Suburban Hot water heater Sw10E
First, you can operate your water heater with either propane, 120V electric, or with both together. They are actually designed to operate together. The thermostats are designed such that the electric heater turns on at a slightly higher temperature than does the propane, but both turn off when the water reaches 140 degrees. By designing it this way, if you have both power sources available, the 120V side will maintain the temperature of the water to keep hot water available to you. when hot water demand is high, like taking a shower or using a washing machine, the electric heater turns on but the temperature of the water continues to fall, since it can not keep up with the water demand. At 5 to 10 degrees below the temp. set point of the electric element, the propane turns on and it too heats the water.
By doing this the supply of water available is greatly extended and it still will only use propane when hot water demands are high, but not to maintain or even to fill a sink or pan. In that manner the propane use is minimized and the available supply of hot water is maximized. You can also operate on either supply, alone and if you have 120V power this can be done to extend the life of your propane tank fill or because electricity is included with the site rent.
As to the switches, there will be an on/off switch with a small light over, or near it for the Suburban water heater. That comes as part of the install kit from Suburban and is pretty standard. When that switch is on it operates from propane and the light will tell you if the propane should fail to light. But the switch for the 120V power is one that was supplied by your RV manufacturer and so could be most anything that they may have installed. The Suburban supplied switch can be found on the inside of your water heater access panel and it must be on to use electric heat but there is frequently a second switch inside of the RV which is supplied by the RV manufacturer.
Once you know for sure which switch it is, simply turn that switch on to enable the 120V heater to operate and using both at the same time is just fine. Is that outside switch that you mention located inside of your water heater? If so, most likely it is for the 120V heater. To check it, just leave the propane turned off and turn on the mentioned switch and wait to see if the water gets hot.
If you tell us what make and model your RV is, that would tell us a great deal more about what you actually have.
