The Standard Hot Water Heater and the Water System

I have received questions from readers and also have encountered similar questions on regular RV forums from new RV owners about how the hot water tank works. While I have written about that in various other articles usually about something else, I thought that perhaps while we are just about to get started - at least hear in the Northeast - with the RVing season and de-winterizing, it might be good to devote one easy to find article about this. (At the writing of this article I have still not dewinterized. The temperatures are just evening out and sometime this week I hope to be able to do it.) And since the standard RV water system should be looked at as a whole, I will also go into the basics of that as well. Now, I say "standard RV water system and standard hot water heater" as this does not pertain to any of the new innovative hot water systems that Roadtrek is now using on the newest models. This is about the propane fired Suburban Hot Water Heater with its hot water tank.

OK - the water system is basically the same from RV to RV and Travel Trailer. You have a "city water" connection that you can hook up a hose to and have water running in your RV. And you have one or more water tank that will hold clean water for you to use in your RV when you don't want to hook up a hose. First, we will look at using the hose which is referred to in RV language as using "city water". When you connect the hose and turn it on at the outside water spigot water will go through your entire water system including your hot water tank. The hot water tank will fill and at the same time water will fill all of your plumbing in the RV. To use water, you just go inside and turn on a faucet or flush the toilet and water will flow. You do not turn on the water pump.

For those times that you don't want to be bothered with having to hook up a hose to use water in your RV when you are out traveling in it, there is the fresh water tank(s). With the Roadtrek there are various places that Roadtrek has placed a tank fill hole. That hole in many Roadtreks is in the inner door frame that the driver's door closes into. With the Roadtrek there is a plug cap - usually orange - that you pull out and set aside so that you may put a hose up to the hole and fill the tank. One thing to keep in mind is that if water is going to go into the tank, then the air in the tank has to come out - so if you find that the process of doing this causes the water to back up and out the fill hole long before the tank is full, get yourself a water tank fill tube sold in many RV shops. All it is is a clear plastic flexible tube attached to a fresh water hose connection with a shut off valve on it. The end of the tube should be cut at a 45 degree angle. If it is not, cut the angle into it yourself - and sometimes a slightly greater than 45 degree angle works even better. Don't push that tube down into the fill hole. Look into the hole and you will see that it will take a slight bend. Turn on the water to the hose, but at much less than full force. Put the end of the tube just before that bend with the open end of the cut angle facing down into the bend. Turn on the valve on the tube and the water should flow nicely down with plenty of room around the tube for the air to escape at the same time. When the water now backs up and out of the hole, the tank is full. It is helpful to have someone checking the tank's fill progress at the wall panel monitor and tell you when it reaches the top. You will also hear the water coming back up and can tell from the sound when to shut off the valve on the tank fill tube. Your fresh tank is now full. 

When you are going to use the water from your tank(s) and not use "city water" you must turn on your water pump switch. The water pump runs on 12 volt battery power from your coach battery. So you need to turn on the battery switch before you turn on the water pump switch. When the water pump switch is turned on and you open a faucet or flush the toilet you should here the pump start to hum and it is working pumping water. Some are quieter than others. IF the hot water heater tank is empty, it will also start to fill the hot water tank. The Suburban hot water heater tank usually holds six gallons of water. The water pump does not flow as fast as a city water hose connected to a water spigot outside so it will take a little time for the water to fill the hot water tank. How do you know itis full? First, DO NOT TURN ON THE HOT WATER SWITCH! Just turn on a hot water faucet handle. Air will come out first and then water will come out in spurts. When water flows steadily, the hot water tank is full.  NEVER TURN ON THE HOT WATER SWITCH IF THE HOT WATER TANK IS EMPTY. You will burn out the hot water heater!
 
As soon as the hot water tank is full, you can start turning on the necessary switch to ignite the hot water heater and the heater will heat the water in the hot water tank. You don't use any matches to light the hot water heater. It is done electronically. You may be able to hear the flame of the hot water heater ignite with propane inside. You will definitely be able to hear it burning if you go outside to the hot water heater vent. If it is dark enough you will see the flame. You should be able to hear the hiss of the gas burning. This area gets hot so don't touch the vent cover while the hot water heater is on. It also takes some time to heat six gallons of water. At home if you put a pot with six gallons of water on the stove it will take some time to heat - the hot water tank is just a big pot of water on a burner too.

I have not talked about the hot water heater bypass valves and I am not going to go into that here. You MUST make sure that the hot water heater bypass valves are set to ALLOW water to flow into and out of the hot water tank. This article here will tell you about the hot water tank bypass valves and dewinterizing to put them into hot water use mode. Other RVs will have different setups. Some don't have bypass valves at all. Some have bypass valves that were aftermarket installed.

Now to understand how the hot water tank works, you must understand this. Water does not come out of the hot water tank unless you open a hot water faucet at the RV sink. As water comes out of the hot water tank, more water comes into the hot water tank re-filling it. When the hose is connected and water is coming through the hose into the RV the water pressure from the hose is what moves the water inside your RV pipes - and  When using the fresh tank, it is the water pump that moves the water in the pipes and in and out of the hot water tank. 

It is simple - for water to move out of the hot water tank and into your faucet and into your sink, water must go into the hot water tank to push the water out from the hot water tank. 

You cannot drain your hot water tank empty through a sink or shower. The hot water tank will ALWAYS be full. If your hot water stops coming out with the faucet open and the water pump on it means that your fresh tank is empty. The hot water tank is still full. Why? Because there is no water to push the water out of the full hot water tank. This is not easy at first to get. Think about it for a moment. 

If  you want to empty your hot water tank you must drain it by opening the hex head of the anode rod OUTSIDE where the hot water heater is. This rod is also the drain plug. This is the only way to drain and empty the hot water tank.

As long as you are using the RV though the season and you don't mind the water sitting in the hot water tank between trips you can just leave it there. It will be heated every time that you use it and that should kill any bacteria that might form in the water - and generally you are not drinking hot water from the tap, but that is up to you to decide. You could certainly go out and drain it after a trip. We don't.  

It is all just water goes in for water to come out of the hot water tank. When you fill your fresh tank and the hot water tank then fills, you are losing six gallons of fresh water from your fresh tank. So if you have a 24 gallon or more fresh tank, subtract from that capacity the capacity of your hot water tank which will always hold that water. Go back and fill the fresh tank again with the hot tank full and you regain that water to use.

Yes, it is confusing. There are many RVers who don't understand it or just don't know this. 

Do you need to leave your hot water switch on all of the time when you are in the RV? We don't. I only put it on when I need to use hot water. The hot water switch only turns on the heater. (I also only turn on my water pump switch when we need to use the water - though we keep it on overnight.) Once heated that day, the water will maintain a hot or at least warm temperature as the tank which is inside is heavily encased in insulating foam and holds heat in. If the water is just warm or has gone cold just flip the switch on and wait a minute or two for it to heat back up. If you are taking a shower remember that six gallons can come out faster than your think and water replacing it has to heat so you may find you are taking a cold shower toward the end. 

That is the basic course in standard RV water systems. It is actually no different from the water system in a house. In a house we don't think about these things until something is wrong. We just turn on the faucet and expect water and turn on the hot and expect not water. Not very different in an RV - it just needs more hands on to get it there.