RV Hot Water Heater Guide: How to Operate, Fill and More


Your RV hot water heater is the essential appliance that delivers the comfort of home to your camping experience. Having hot water available to shower, wash your hands, clean dishes, and many other tasks is priceless. Whether you’re operating a propane, electric, tankless or small tank hot water heater this guide covers all aspects of this amazing RV companion.

Every RV owner should be familiar with how their water heater works. This includes filling and draining the unit, how the electrical controls work, replacing the main components and more.

Some specifics vary depending on the exact brand and style of water heater you have, but many of the key concepts are standard for almost all RV water heaters.

Whether you just got your first RV, upgraded to a newer model, or are having troubles with your current water heater, you’ll find everything you need to know right here.

RV Hot Water Heater Basics

Most RV water heaters will either be a 6-gallon or 10-gallon tank, although tankless heaters have become more common in recent years. 

Tankless Hot Water Heaters

Hot water heaters that are tankless are also referred to as “on demand” units. These can use propane or electricity to power a heat exchanger in the unit, which warms up the water as it passes through. The only water in the unit is the small amount waiting in the internal piping, this is why it’s considered “tankless”.

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On Demand Operation

When you turn on your hot water tap you’re creating a “demand” for hot water. Once the unit senses the flow of water through the inner piping the heating elements automatically turn on and begins to warm the water. 

In the short time the water takes to travel through the series of internal pipework it warms up to a temperature suitable for washing and showering.

Once the hot water tap is turned off at the faucet the tankless heater senses the stoppage in flow and turns off the heating element to conserve energy. There is no longer a “demand” for hot water at this point.

Pros and Cons of Going Tankless

In theory, tankless hot water heaters can provide a continuous flow of hot water for showering, cleaning and whatever else until it loses power or its supply of propane. This is one of the major advantages over a traditional tank style of water heater that needs to be preheated before use and is usually reduced to providing just warm water during heavy use.

Some of the other major advantages include the energy efficiency which is a big deal in an RV, saving fuel and electricity are essential when operating off grid. Physical size is another advantage of tankless hot water heaters, they tend to be much more compact units compared to those with a tank.

The biggest drawbacks to this style of hot water tank is the price tag. There aren’t many models that can retrofit into a 10gal tank space and the ones that can are expensive in comparison.

They also tend to suffer from more issues and breakdowns though the technology is always improving.

Lastly, because the water is heated as it moves through the unit it’s common to switch to a low flow shower head to add back pressure and make the water travel slower through the heater. The lower the GPM rating, the lower the flow rate has to be.

Hot Water Tank Heaters

RV hot water tanks typically have a 6-10 gallon tank or reservoir to hold water during the heating process, similar to what is commonly found in homes. However mini-tank water heaters have recently hit the market providing a “point-of-use” option which get installed and connected directly to a sink or shower.

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Hot Water Tank Operation 

Whether the hot water is being used or not, the control unit will hold the water in the tank at a specific temperature as long as power and fuel are available to it. This temperature is measured by a sensor in contact with the water in the tank. 

Once the sensor detects a drop in water temperature it sends a signal to the control module to turn on the heating element. This can be due to the water sitting around and cooling down over time or because the hot water is in use drawing it out of the tank and cold water is entering the tank in its place.

Initially, the water coming out of the tank will be at the ideal temperature for normal use. After heavy use the heating element can have trouble keeping up with the demand for hot water resulting in only warm water being available. At this point postponing tasks that require hot water for 15 minutes will give the tank time to return to maximum temperature.

Benefits of a Hot Water Tank

Traditional hot water tanks are less expensive than a tankless alternative and they’re pretty bullet-proof when it comes to reliability. 

Electric Water Heaters

If your RV has an electric water heater, your heating element will cycle on and off as it needs to in order to maintain the water temperature, which means you don’t have to turn it off when it’s not being used.

Electric water heaters have the advantage of conserving your propane and more efficiently keeping your water at the desired temperature. If your water heater doesn’t have the ability to switch back to propane when you’re not on shore power you’re not going to be able to boondock without running your generator for hot water. 

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  • INDEPENDENT INSTALLATION: 36-37" cord plugs into a 120 volt outlet for independent installation or in-line with a large hot water source

Propane Water Heaters 

Unless you’ve sprung for a top of the line RV, your hot water heater probably runs on propane. Like all other propane appliances, it requires lighting a pilot flame. In some RVs this will be done manually with a lighter once you’re parked and leveled, but most newer RVs will come with a direct spark ignition.

To use direct spark ignition, simply turn on your water heater. The thermostat will sense if the water needs to be heated, and if it does the control circuit board will open the gas valve while also using the igniter to create a spark in the front of the gas burner tube. Once the water has come up to temperature, the water heater will automatically turn off.

The major advantage to a propane generator is that it won’t drain down your RV house batteries. Except for a tiny bit of electricity to run the control circuit, a propane water heater will work with or without shore power. This makes it perfect for RVers who plan to camp in more remote areas rather than campgrounds and holiday parks.

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Filling your Water Heater

The first time you go to use your water heater or if you’re about to use it after winterizing, you’ll need to fill the tank with water before turning it on. The manual for your specific model will have the recommended water levels to fill it to, but you can also just play it safe and fill the tank completely.

If you have a bypass or drain on your water tank make sure to close it before you begin filling it. Filling your hot water tank can be done using the water from your fresh tank and the RV water pump. It can also be done using the water pressure supplied from city water connected to your water hook up.

With all your plumbing connections tightened to prevent leaks, open the hot water taps on all your faucets. This will allow the air volume trapped in the tank to leave and water to enter and replace it. You’ll know the hot water tank is full when water is coming out of all your faucets. The water won’t be warm yet but it will let you know it’s safe to turn your water heater on without damaging the element.

How to Operate Your Hot Water Heater

Your hot water heater requires electrical power even if it runs off propane. There are a few different parts of your electrical system that need to be turned on in order for it to function.

Electrical Panel

There should be a fuse or circuit breaker to provide power to your hot water heater, this will power the electronic control board, the igniter and the element if your water heater is electric. The CB will have to be in the “on” position or the fuse installed and in working condition for the water heater to operate.

On/Off Switch

The next level of control is an on/off switch that will be located on a main control panel or near the unit. Put the switch to the on position, there will usually be an indicator light illuminated to show that the tank is turned on.

Propane Supply

If your water heater is propane you’ll need to make sure the propane supply is turned on at the main tank. There may also be a shut off valve near the hot water tank that needs to be turned to the open position.

Once the on/off switch is turned on, you’ll probably be able to hear the igniter clicking and possibly even the flame burning. The indicator light should also be illuminated. 

It usually takes between 20 to 35 minutes for your tank to heat up depending on its size, the temperature of the water inside the tank and also depending if you’re using electric or propane to power it. Electric tanks tend to heat it up slightly faster.

Temperature Adjustment

Most RV water heaters don’t come with the option to adjust the thermal limit switch, instead you have to become a mix master with the cold water in order to get your desired temperature. Having said that, you can replace that thermal limit switch with an adjustable thermostat if you want. 

It’s not a bad idea to consider because with an adjustable thermostat you can save lots of propane by setting the max temperature closer to lukewarm than lava hot, and swapping out the parts isn’t too hard of a DIY project to take on.

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Conserving Water and Energy

Your water heater in your RV is likely much smaller than the one in your house, so paying attention to how and when you’re using your hot water will keep you from running out when you need it most.

For example, if you use a bunch of hot water to do the dishes but immediately turn around and jump in the shower, you’re not going to have as long as you may like to enjoy that shower. Trust me, I’ve learned that one from experience.

How to Drain Your RV Hot Water Heater

Just like when you’re inspecting the anode rod, you’re going to want to turn off your water heater and then open up the pressure release valve before you try to drain it. This will keep you from getting shocked or burned during the process, both of which I don’t recommend. 

By opening the pressure release valve at the top you’ll make sure you’re not shooting high pressure water at yourself when you take out the plug, and once the tank is equalized then go ahead and unplug it. The water will drain out and this is also a good time to flush out the tank. In addition to using the flush wand mentioned above, you can also turn on the city water again for a few minutes and let it flow in and out of the tank. 

Once no more water is flowing out of the tank, put the plug back in and close the pressure release valve. You may want to use a hose to spray off any debris that may have come out of the water heater off of the outside of it before closing the panel door, but otherwise your water heater should be good for your RV to be stored, winterized, or sanitized.

Draining your hot water tank is just one of the many steps in preparing your RV for storage. Check out our guide to winterizing an RV for the rest of the steps to ensure it’s ready and problem free in the spring.

Basic Hot Water Heater Maintenance

The first thing you’ll want to do is to make sure you shut off the power to your hot water heater before you try to do any sort of maintenance, then empty out any hot water that is already inside the tank following the method described above. 

In general, propane water heaters will require a little more upkeep than your electric ones. This is mainly because you’ll want to clean out the burner tube annually to make sure there’s no debris that is blocking your gas flow. 

Checking The Anode

In all tanks you’ll want to check the condition of your anode rod at the beginning and end of every season. The anode is the metal rod that is designed to corrode instead of your tank’s inner walls. Before you service the tank be sure to turn off power to the tank and let the water inside cool for an hour or two. 

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The first step is releasing the pressure in your hot water tank. This can be done by opening the pressure release valve on the outside of the water heater, or by opening a hot water tap in your RV with the pump turned off and the exterior hose disconnected from your outside connection. 

You’ll probably need a 1-1/16 socket and a wrench to remove the anode rod, it will be located near the bottom of the tank and accessed from the vent door on the outside of your RV. 

As you loosen the rod bolt water will start draining from the tank slowly before gushing out once the rod is fully removed. Prepare to get a little wet. If your rod shows heavy signs of corrosion, it’s best to replace it with a new one. 

Once your water heater is drained, you can also use that great opportunity to clean and flush out any sediment and debris in the tank by using a flushing wand. 

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Replacing The Heating Element

At some point along your RVing adventure it’s possible that the heating element in your electric water tank will need to be replaced. This process is similar to replacing the anode. With power removed from the appliance, release the pressure and drain the tank using the method described above. 

Once drained, loosen the terminal screws and disconnect the wires from the element noting the positions. Remove the element with a wrench and replace it with a new one. Reconnect the wiring and refill the tank before applying power and turning it on.

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Replacing The Electrode

The electrode or igniter creates the spark that ignites the propane. If your water heater uses a 2 prong electrode it may simply need to be cleaned. A dirty electrode will prevent the spark from jumping between prongs and igniting the fuel. The same can happen with a single prong electrode but the spark jumps to a nearby metal surface rather than a second prong.

To remove the electrode unplug the wiring and remove the screw holding it in place. Inspect it to see if the tip is blackened or dirty. You can use steel wool or a fine grit sandpaper to clean off the electrode tip and reinstall it to see if it functions. Otherwise replace the electrode with a new one following the reverse order in which you removed the old one. 

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Closing Thoughts 

You got your RV because you wanted to bring some of the creature comforts of home with you on the road, and knowing how to fill, drain, operate, and maintain your water heater will help make that experience even better.

Beau

Beau is an electrical engineer with a knack for DIY repair and construction. When he's not tinkering with his projects he's on the road travelling and enjoying an exciting lifestyle with his young family.

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