How Do RV Water Heaters Work?

Contributor

Tucker Ballister

Favorite Trip

5 Months Solo on the Road

Home Base

Hendersonville, NC

Favorite RV

2008 Fleetwood Bounder

About Contributor

Tucker Ballister is our Content Strategist. He’s a lover of the open road and the proud owner of a 2021 Sunlite Classic travel trailer (his 3rd RV to date). Check out more of his RV adventures, gear reviews, and outdoor advice at thebackpackguide.com.

Your RV water heater supplies hot water to sinks and showers inside (and potentially outside) your RV. If you want a hot shower after a day of outdoor adventures, you’ll need your water heater to function efficiently and effectively. When it works as designed, you probably won’t spend much time wondering, “How do RV water heaters work?”

But when something goes wrong, your knowledge is your most important troubleshooting tool. Understanding how water heaters work in RVs will also help you use and maintain them properly. So, let’s cover the basics of RV water heating systems.

Types of RV Hot Water Heaters

Variety of tankless and tank style RV water heaters
Photo by Camping World

There are several types of RV water heaters, mostly distinguished by their power source. The most common is a gas/electric model, followed by electric only and gas only. There are also tankless RV water heaters, also known as instantaneous or on-demand water heaters. Let’s look at each below.

Gas Only

Gas-only models are powered by propane. They are the most cost-effective units to purchase and run. Although you can use them at the campground, they are also great for off-grid use where electricity is not as attainable. They are available with a manual or electric pilot. 

Electric Only

Electric-only models are powered by 120VAC, so you’ll have to be hooked up to shore power or a generator to use them. Since you’ll be plugged into shore power, these are great for those who spend most of their time at the campground. 

Gas/Electric

Gas and electric models are fueled by propane and 120VAC electricity. They are also called “hybrids”. Like RV refrigerators, these water heaters allow you to maximize your resources for the best efficiency. When on shore power, you can switch to electric. When boondocking, you can use propane. You can also use both gas and electricity for greater efficiency. 

RV Tankless Water Heater

Tankless water heaters are becoming increasingly common on new RVs. Also known as “instantaneous” or “on-demand” water heaters, they heat water as it passes through a coil. They can be gas or electric, but gas is most common for RV use. Although often used, the term “instantaneous” can be misleading, as there is still a 20 to 30-second delay in getting the water heated and through the pipes to the faucet.

Another reason for the popularity of tankless water heaters is their size. Compared to a standard RV water heater with a traditional tank, they are much more compact, allowing for more mounting options. In addition to size, switching to tankless will save you a considerable amount of weight.

Where to Find Your RV Water Heater

The location of your RV’s water heater depends on the manufacturer. Most place them on the off-camp side, opposite the main entry door. However, your water heater’s location can be towards the front or back of your RV if you have a rear kitchen or front kitchen floorplan.

Here’s an example of what your water heater’s exterior access panel may look like:

Exterior Dometic RV water heater access panel
Photo by Camping World

Here’s an example of a water heater tank and plumbing lines from the inside of an RV:

Inside view of cabinet with rv water heater
Photo by Camping World

Knowing where all your RV components are located is generally helpful. This is especially true for water heaters, as you need to know where to drain an RV water heater.

How Does a DSI RV Propane Water Heater Work?

Forest River control panel
Photo by Camping World

Ensuring the tank is full is the first step in operating any water heater before turning the water heater on with your RV’s control panel. If you have a gas/electric model, you can heat water in the tank with propane or the electric element. You can also employ both for quick hot water recovery. 

Propane is the primary heating source for gas/electric models. The propane is burned at the end of the burner tube, and the flame enters the flue tube. Heat and exhaust gasses are carried through to an exhaust vent at the top of the water heater.

Here’s the sequence of operation when your water heater uses propane:

  1. The propane control switch is turned on.
  2. 12 VDC goes through the thermostat – a normally closed switch.
  3. The thermostat demands heat, and contacts close, opening the propane valve.
  4. The spark ignites the gas in the burner tube.
  5. When a set temperature is attained (usually 140℉), the thermostat’s electrical contacts open, closing the gas valve.

How Does a Gas/Electric RV Water Heater Work on Electric?

Inspecting an RV water heater
Photo by Camping World

In the electric mode, sufficient 120-volt AC (VAC) power is required to heat the electric element. This mode will only be an option when plugging into shore power or using an RV generator.

Technician Tip: The requirements for voltages, amperages, or wattages are on the data plate or in your owner’s manual.

Here’s the sequence of operation when your water heater uses electricity:

  1. The electric switch is turned on.
  2. 120 VAC goes through the thermostat – a normally closed switch.
  3. The thermostat demands heat and contacts close.
  4. 120 VAC goes through the ECO (energy cut-off) switch, normally closed.
  5. 120 VAC goes to the heating element and heats water in the tank.
  6. When the set temperature is attained, the thermostat’s electrical contacts open, removing power from the electric heating element.

Technician Tip: Steps 2 and 4 may be reversed on certain models.

How Does a Tankless RV Water Heater Work?

Inside view of tankless RV water heater
Photo by Camping World

Also known as on-demand, tankless RV water heaters provide instantaneous hot water. When you open a hot water fixture, it triggers the heat exchanger.

Unlike traditional RV water heaters, the burners are only activated when the faucet is opened. When the faucet is turned off, power is removed from the water heater burner.

The water temperature can be adjusted at the control panel, but there is also a redundant energy cut-off (ECO) switch, or “high limit switch,” that monitors the heat. These ECO switches shut off the heat source if the water temperature gets too high and turn back on when the temperature drops back into the set range.

What Is an RV Hot Water Heater Pressure Relief Valve?

All water heaters have a pressure relief valve. This valve is designed to release water and pressure into the air if pressures or temperatures get too high, jeopardizing the heater’s structural integrity or posing a risk of burns to the user. The valve opens when pressure/temperature rises above a set point and closes when it returns to safe levels.

How Much Propane Does an RV Water Heater Use?

RV propane tank inside storage compartment
Photo by Camping World

The amount of propane an RV water heater uses is affected by many factors, the most important of which is type. Tankless water heaters consume less propane than tank-style water heaters. This is because they only heat water when needed, which makes them more efficient. 

Another factor, perhaps the most obvious, is usage. If you have a family of four who each take a hot shower in the morning, you’ll use far more propane than a couple who use theirs sparingly.

It’s difficult to estimate the amount of usage based on these factors, but on average, most RV water heaters will run on a 20-pound cylinder for a few days. That said, this figure will go down if you use your propane for other appliances. 

If you need to extend the amount of hot water you get out of a single cylinder, there are some things you can do. The first is turning your faucet temperature down to the lowest comfortable level. The next would be to use a larger or possibly retrofit a second propane cylinder. Switching from tank-style to tankless will also allow you to conserve more propane.


Hopefully, this has clarified how RV water heaters work. Here are a few more resources to help you use and maintain your RV water heater: 

What questions do you have about how RV water heaters work? Let us know in the comments below.

  • Comment (11)
  • Stratton says:

    My water heater ignites but goes out must I have the hot water turned on when I ignit it’s a 2009 StarCraft

  • Cyrus Juliet says:

    Your gas or electric water heater’s “VAC” setting is a ground-breaking energy-saving innovation. It’s a contraction of “vacation,” suggesting that this technology only operates when the water heater isn’t used for a long length of time.

  • Holly says:

    Great post! Gas Water Heaters truly add a touch of luxury to the nomadic lifestyle. Your blog beautifully highlights the significance of these heaters in transforming our mobile homes into cozy havens, where hot water is no longer a luxury but a staple.

  • Dalton Bourne says:

    Thanks for the inspiration! You show a great knowledge of the subject.

    • Alex says:

      I bought a 2005 Holiday Rambler 28′ 5th wheel used. It had no owners manual. I just hooked water up to it and confirmed nothing leaks and water is flowing. I turned the hot water on in both the sink and shower, which I’m assuming would fill the hot water tank. Although this camper has switches for both propane and electric. So I’m not sure if there are two different tanks, or what? Currently I only plan to use the electric water heater portion. Should it be safe now to flip it on? Where is the bypass that you spoke of in your article? I guess it would also be wise to check the anode bar as well to ensure the previous owner didn’t let it fully corrode. I’ve had to fix numerous things in this camper as it appears the previous owner neglected some maintenance.

      • Hi Alex,

        To solve your first issue, I’d recommend heading to the Holiday Rambler site and downloading a digital version of your RV’s owner’s manual: https://www.holidayrambler.com/owners-manuals/

        Here are a few answers to your other questions:

        Q: I’m not sure if there are two different tanks, or what?

        A: There are not. Your water heater should have a single tank, but it can be heated using propane or an electric heating element.

        Q: Should it be safe now to flip it on?

        A: It’s safe to turn on your water heater if you’re connected to city water or your fresh water tank is filled. The only danger to turning it on is when you know the heater’s tank is completely empty.

        Q: Where is the bypass that you spoke of in your article?

        A: Depends on the exact make and model. You’ll usually find the bypass valve on the plumbing lines just outside of your water heater’s tank. But finding the proper owner’s manual is recommended before troubleshooting further.

        Hope all of that helps!

    • You’re most welcome!

  • Bruno John says:

    Your RV water heater has a problem when the DSI fault lights up stays on for a long time. It is commonly not extreme, and a little troubleshooting can usually do the trick.

  • Ross Elliott says:

    I have a suburban gas elec 21lt heater with a red and green wire coming out of it where do they go on the 12v switch and on the same switch where does the 12v wire go cheers

    • Hi Ross!

      Do you know the model number on that unit? It should be located by opening the access door on the outside of your RV.

      With that info, I can try to track down the wiring diagram for you.

      Hope that helps!

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