Just a few basics for anyone else who may read this thread later on in life. There are SIX posts in this thread, and please read all six.
WARNING: Always make sure the water heater is full of water before using it either by propane or the electric heating element. This is explained in more detail below:
The Suburban SW6DE model number means you have a 6 gallon water heater that has a Direct Spark Ignitor (D.S.I.) and an Electric powered heating element. The following also applies to the SW10DE, SW12DE, and SW16DE models. This water heater can be powered by propane, electricity, or both at the same time. You can use the electric option when you are at campsites that have electricity, and the propane option when at places that don't.....or a combination depending on your needs.
Airxcel | Suburban Manufacturing Service
Operating on propane
If using the water heater on propane, you must first make sure your propane tanks have fuel, the valves are open, and the lines aren't full of too much air going to the water heater. You can usually turn on your stove in the camper and this purges a lot of air from the lines first.
You will now turn on your Direct Spark Ignitor (D.S.I.) switch inside your trailer/coach. Your particular RV may just have a switch that says water heater, heater, htr, or heat (and may be by itself or in a panel of other switches). It can also be on a digital touchscreen panel if equipped. The DSI is a low voltage ignitor (12 volt DC power) that takes the place of the old fashioned pilot lights that gas powered water heaters have. You can usually hear a rapid clicking sound at the water heater as the DSI is making sparks to ignite the propane. By not having a constantly on pilot light that burns all the time, the DSI is safer and uses less propane.
You just leave the DSI switch on, and whenever the water heaters thermostat calls for heat using propane, the DSI will provide the sparks to ignite the gas. If you turn the DSI switch off, then you won't be able to use the propane option.....thus turning off your water heater using propane.
The DSI uses a 12 volt current (DC/battery) to make sparks which lights up the propane to start the burner to heat your water. If the DSI system fails to light the propane after a set number of attempts/time, you will get a fault and the system shuts itself off (including propane). If you keep getting faults you may have a propane delivery problem somewhere. My switch has a fault/reset light next to it that illuminates until the propane ignites, which can take a few attempts. Once the propane ignites, the fault/reset light goes off.......................but after so many failed attempts the whole system locks itself out and won't retry to light (the reset/fault light will stay on). You can reset the lockout by turning the switch off and back on after about a minute. If there is air in the propane lines, you may have do this a few times.
Operating on 120 volt electricity
Now for the 120 volt electric option. Some trailers/coaches MAY have another inside switch to turn the electric heating element on (See post # 4 below for information on the SWDEL model)
, which this element is located inside the water heater. This element works only off of 120 volt AC power, and you must be plugged into some form of 120 volt power for this heating element to work.
However, many (including all of my trailers), do not have an inside on/off electric heating element switch......but this black switch is located on the front of the water heater itself...near the left hand bottom side. It is hidden just a little. You will have to open/remove your outside water heater panel to get to this switch. The switch may also have a hairpin cotter pin thru it that prevents it from accidently getting turned on, that you will have to remove first before you can use it....or can also have a piece of foil tape over it. See pic below, which shows the switch in the ON position
And here is a pic with the cotter pin installed, with the switch in the OFF position.
Now, if you turn on the electric heating element, you must always make sure the water heater is full of water first. If you turn it on and there isn't water in the heater, the element will burn itself out in a matter of seconds, usually before you can even say "OH CRAP", and turn it back off. (EDIT UPDATE 11-2-17: Suburban now installs a new type element that will last longer before burning up in dry-fire scenarios. See post #6 below)
Probably the easiest way to verify there is water actually in the water heater, is to briefly flip up the lever on the temperature/pressure relief valve at the top of the water heater (pic below). If water comes out here, then the heater should be full of water. Just turning on the hot water faucets inside the RV, cannot be a trusted way to verify. If you have your water heater bypass valves still in the winterization mode, then the cold water line is actually merged into the hot water line, and you will get water out of the hot water faucets.......but it's not coming from the water heater, which would be bypassed and dry inside....and since it's dry, you'll burn out your electric heating element if you turn the switch on. (See post #3 below for more information on bypass/winterization valves)
WARNING: In case the water is already heated, DO NOT stand directly in front of the temperature and pressure relief valve when flipping up the lever. Stand off to the side so you don't get splashed with possible hot water.
When using this switch, it's a good idea to make yourself some kind of tag or something to remind yourself it's on (and to turn it off when breaking camp/draining water lines). Many, many a camper has forgot to turn the element off, when breaking camp. They drain their water and/or heater, and pull their trailer home. When they get home they plug back into shore power and IMMEDIATELY burn up their electric heating element. You can easily use a clothes pin and write WATER HEATER on it with a sharpie. Just attach this clothes pin to your RV's coupler hitch when you have the electric heating element turned on, and it will remind you to shut it off before you can attach your trailer to your truck. You can leave the clothes pin in the water heater compartment when not in use.
If you do burn the electric heating element up, you can still most likely use the water heater on propane only. Sometimes though, with a burned up heating element, it will trip your breakers in your trailer.
You can power your water heater by propane with the DSI making sparks to ignite the propane....as well as using the electric heating element (as long as you have a form of 120 volt shore power/generator) at the same time and get the fastest heated water.......or either one individually. Just remember that if there is only one switch inside the RV to the water heater, it is going to ONLY control the DSI/propane side of the water heater. The switch outside on the face of the water heater ONLY controls the electric heating element.
According to Suburban, the electric element has a recovery rate of 6 gallons per hour, the propane burner has a recovery rate of 10.2 gallons per hour.....and if you use both at the same time, the recovery rate is 16.2 gallons per hour.
The door to your water heater, that is accessed from outside of the RV, should look similar to the one pictured below. It may be painted to match the color scheme/striping of your particular RV.
Around the 2002 model year and later, the Suburban water heater came stock with a 1440 watt electric heating element. What this means is it will take 12 amps to power it with 120 volts, when the element is on and heating the water. You may need to keep this in mind when hooked up to 30 amp power supplies, as it may cause breaker(s) to trip if you exceed the maximum amount of amps on a circuit. You may need to turn the electric heating element off... if using other high amp 120 volt appliances at the same time, like microwave, air-conditioning, coffee pots, hair-dryer, etc.....as you would only have 18 amps available to power these other things. (30 amps total minus 12 amps for the heating element = 18 amps available)
In other words 40% of your available power is going to the electric heating element when using 30 amp RV's/power supplies.....but this only applies while the element is energized. Once the water is heated, then the thermostat will turn off the electric element until the temp of the water falls enough that the thermostat turns the electric element back on(energizes) to begin the heating process again.