Originally Posted by f1100turbo
Turning on the hot water Tap may be a false indication that there's water in the tank.
Here's a pic.
I open this while filling tank to bleed air and make sure it's full.
"Sabre owners united"
It looks like you've gotten a lot of good advice from experienced members here.
+4. If the bypass valve (which ties the cold water line into the hot water line) has been set for winter mode, or is faulty....you WILL get water out of the tap when turning the hot water tap on....but it's coming from the cold water line and not the heater tank. This is a false indication of there being water in the heater itself.
Also, if you do turn on the electrical heating ELEMENT, when there is no water inside the heater, it will burn itself out. I think you confused the term and said anode. The anode rod is a different animal, and is a rod that goes inside Suburban brand water heaters, that keeps the tank from rusting out.
Once you gain experience and know for sure all about the bypass valves and such, you probably can just turn on the hot water tap to see if water comes out as an indication of there being water inside the heater. BUT the only 100% sure way, and safe practice technique, is to do as Turbs pointed out.
I do need to add, that you must be hooked up to either a city water supply, or have a pump pressurized system in order for water to come out of the pressure relief valve as KyDan pointed out.. If you just walked out to your camper and opened the pressure relief, with no form of pressure going to the water heater, you probably wouldn't get much water to come out, even if the heater tank is full. The pressure relief valve is at the TOP of the tank, so without pressure, gravity will work against you.... and not push water out the valve.