As ScottG said. The "TANK HEATER" switch should be for anti-freeze heaters on your holding tanks. It is not related to heating water for use and will not noticeably warm water in any tank, only (hopefully) keep it above freezing. It should only be on when needed to prevent freezing.
The panels in many RVs are poorly labeled and to make things worse, there is usually more than one water heater switch. Sometimes they install switches for both gas and electric on the inside panel. Usually when they install both switches on the same panel, they do a slightly better job of labeling them. Some Fleetwood panels have both switches and some don't. If it just has one switch labeled "Water Heater" it is almost always the propane water heater switch.
I said usually a lot in that first paragraph. Unfortunately, not all water heaters are the same. Pretty much every RV water heater has propane heat. Most newer ones, and a lot of older ones, also have an electric heating element. Again, unfortunately RV manufacturers sometimes put an electric water heater switch on the control panel and sometimes they don't. Fleetwood has done it both ways. IF it has an electric element, and being a 2013 it very likely does, and it doesn't have a switch on the panel labeled "ELECTRIC WATER HEATER", then the switch is probably located inside the access cover on the outside of the water heater. It's often not labeled and is just a black electric switch, possibly with a 0 and 1 or on and off. It's also often hidden at the bottom if the unit tucked away next to the gas valve partially hidden by the burner tube.
As others have suggested, its important to make sure the heater's tank is full and has not been bypassed before turning it on. Turning on the electric element without water in the tank will likely burn out the element very quickly. The easiest way to verify the tank has water is to either turn on the water pump if not connected to pressurized "city water" or make sure the pressurized water is hooked up and turned on. Then release the OTP (over temperature pressure) valve on the outside of the water heater. It will have a metal tab handle that you lift to release. If water comes out, your tank is full. If you hear water running in and air comes out, hold it open and let the tank fill until it runs out then release it. If no water or air comes out, the tank has been bypassed.
Once you verify the tank is full, ensure the propane is on and the lines have been purged of air. You can ensure the lines have been purged by lighting a burner on the stove and letting it burn for a minute. If it burns steady, the line is cleared of air. Now turn on the "Water Heater" switch on the panel. You should hear the igniter sparking and the flame should ignite and stay lit. If it tries to light and goes out, it should try again. After some number of attempts to ignite it (usually 3) , if the flame doesn't light and stay lit there is a problem with the heater. There should be a red LED near the water heater switch labeled "DSI FAULT". After the per-programmed number of attempts and failures to light/stay lit, this LED should lite and the heater will not try to light again until it is switched off and back on. This lockout is a safety mechanism to prevent excess propane from building up and suddenly igniting. If it is locking out, there is something wrong with the heater and more troubleshooting is necessary.
Assuming the RV is equipped with an electric element and you can find the switch, you can turn it on (don't forget to turn it off before draining the heater). This will take longer to heat the water than gas, but not excessively long. Some units will an indicator light or lighted switch to show when the electric element is on but many don't. You may or may not be able to hear something as the element heats but there are no other indications that the electric element is working other than waiting and testing the water temperature. We almost always use only the electric element although I try to run the propane occasionally to keep things working.
You can use both propane and electric at the same time or either one independently.
Mivy wrote:
Could it be that it will work at 30 amp once we get to campground?
See above for detailed description of how to check things out. Specifically with regard to this question, the switch you referenced is for propane operation so should not rely on 110V electric at all. It will require 12V power for the control board and spark ignition to work. This is provided by the batteries when operating without AC power and/or power converter when plugged into AC power.
For the electric element, assuming it's so equipped and you find the switch, it will require roughly 13 amps to operate. If you are powering your RV using a standard 110V extension cord from a typical 15A outlet, it should still work although it wouldn't work if you tried to power anything else like the microwave or air conditioning. If it doesn't work, you will know because it will trip the breaker feeding the outlet and you will no longer have power for any 110V items (TV, microwave, air conditioner, etc...). For RV's with 30A service, there's no difference (other than the amount of current available) between powering it using an adapter cord to plug into a 15A outlet and plugging into 30A. For RVs with 50A service, there are some technical differences, between 50A and adapting to 30A but for the purposes of your question there are no practical differences. If the breaker doesn't trip it should work as well as it will in an RV park.
