How To Fill RV Hot Water Heater? (Easy Guide)

Without an ample supply of on-tap hot water, an RV is incomplete. Bathing and washing dishes in cold water are one notch down from meeting two flat tires, so any RV worthy of the title comes equipped with a hot water heater.

Hidden away in the bodywork of your home on wheels is your trusty but sensitive RV hot water heater – here’s how to fill it and treat it right so it can do right by you!

An RV hot water heater can be filled by piping pressurized city or campground water directly into the RV’s plumbing system, or pumping water from the RV fresh water tank into the hot water heater tank using the RV’s water pump. Fill the water heater tank before switching on the electric heating element.  

To ensure your RV’s water heater produces a reliable supply of hot water, it’s essential to know how to safely fill its tank, use its power sources, and maintain its vital organs.

RV water heaters are complicated appliances, and many RV owners choose to ignore them until they fail. Without proper use and routine maintenance, an RV water heater will cease to operate.

The Best Ways To Fill An RV Water Heater Tank

When RVing with a city water hookup, protect the RV plumbing system and water heater by using a water pressure regulator and a water filter. When dry camping, fill the freshwater tank using a flow meter and ensure the water pump works properly to supply the water heater safely.

RVs have complex plumbing – a matrix of tanks, pipes, valves, filters, and faucets that supply hot and cold water to the kitchen, bathroom, and outdoor shower. An equally elaborate drainage pipe and valve system manages the wastewater from the RV’s plumbing system.

Knowing the following design and operation principles will make filling your RV hot water heater a trouble-free experience:

  • An RV water heater is installed into the cold water line, with a hot water line extending from the heater tank to the kitchen, bathroom, and outdoor shower.
  • The water heater will need to be inspected for leaks and filled with water upon arrival at the campsite or before camping off-grid.
  • Never turn on the 120V water heater switch when the tank is empty – a dry tank will destroy the heating element in seconds.
  • How you fill the water heater will depend on whether you’re camping on-grid or off-grid.
  • If the RV was winterized using a water heater bypass valve, the valves feeding the water heater need to be opened to allow cold and hot water to pass into and out of the water heater tank and the bypass valve closed.
  • Outdoor shower faucets must be closed.

Filling Your RV Hot Water Tank When Camping On-Grid

When you set up your RV at a campsite equipped with grid water and electricity, follow these steps to ensure your water heater fills safely:

1.Ensure all 120V switches controlling the water heater are in the OFF position.

The first of these switches will be located in the water heater service bay, accessed from the RV’s exterior by unscrewing the water heater inspection panel.

A second 120V switch for the water heater may be found located on the control panel inside the RV (not all RVs have an interior water heater 120V switch).

2. Attach a water pressure regulator and set it to a safe pressure.

3. Connect a water filter to the regulator.

4. Fit a drinking water hose to the water filter.

5. Connect the hose to the City Water inlet on the RV using a brass right-angled elbow attachment (to alleviate stress on the inlet port mechanism).

6. Open the city water spigot.

7. Open all hot water faucets inside the RV to allow air in the pipes and water heater tank to escape.

8. Leave the hot water faucets open until a steady water flow is released. 

9. Connect your RV to 120V shore power.

10. Turn on the exterior and interior (if applicable) 120V water heater switches.

11. To heat the water quicker, simultaneously run the water heater propane burner and the 120V heater element.

Note: The water heater has a pressure relief valve that prevents the tank from rupturing should the water overheat.

  • The pressure relief valve also serves as an overflow outlet for the hot water tank.
  • The pressure relief valve should not be used as a gauge to determine whether the water heater tank is full or not.
  • Filling the tank using the pressure relief valve as a gauge will compromise the air pocket at the top of the tank that regulates pressure in the water heater tank.

How To Fill Your RV Hot Water Heater When Camping Off-Grid

Off-grid (dry camping) makes you reliant on your RV’s freshwater tank for your in-house water needs, including clean water for your water heater. Having a full fresh water tank is essential when you arrive at the off-grid campsite.

Without the luxury of a pressurized external water source feeding your RV’s water heater, filling your freshwater tank before you reach the campsite is essential. You can do this at a gas station close to your destination to avoid driving long distances with excess weight from a full water tank.

Follow these guidelines to fill your hot water heater for your boondocking escape safely:

1.Attach a drinking water hose with an inline water filter and a flow meter to the external spigot.

2. Insert the hose into the RV Fresh Water Tank port.

3. Open the spigot and monitor the volume of water entering the tank to prevent unnecessary overflow.

4. Turn off the spigot when the tank is full and remove the hose from the inlet port.

5. Ensure the water heater bypass valve is closed and the cold (inlet) and hot (outlet) water valves for the water heater are open.

6. Open the pressure release valve in the water heater (exterior) service bay to remove any air traps, and then close it.

7. Turn on the 12V DC water pump at the interior control panel.

8. Listen for water flow into the water heater tank.

9. The pump will switch off when the tank is full.

10. Open a bathroom or kitchen hot water faucet until the water flows out steadily.

11. Close the faucet.

12. Switch on the water heater propane burner at the interior control panel via a 12V DC Direct Spark Igniter (DSI) or light the burner manually with a long nose gas lighter (if necessary) via the service bay.

13. Open a hot water faucet to ensure the water heater produces hot water before leaving the filling station. If there is a problem, you’ll be closer to help than in the wilderness.

Necessary: Camping off-grid successfully demands a conservative approach when using water, propane, and battery power. Your hot water heater uses all three, so go easy on these vital boondocking resources whether you’re washing dishes or taking a shower.

How Does An RV Hot Water Heater Work?

Most RV water heaters have 120V electricity and propane power. An electric heating element inside the heater’s water tank heats cold water to a specified temperature, as does a propane burner in a steel combustion chamber adjoining the water tank. 

As the water in the water heater tank heats up to the standard 135 degrees Fahrenheit, pressure builds in the tank. The combination of air pressure and rising hot air force the water out of the hot water opening at the top of the tank into the RV’s hot water piping system.

  • The water heater is protected by two cut-off switches (thermostats) that prevent the tank from rupturing or exploding due to excessive heat and temperature. 
  • Should the temperature and pressure in the tank exceed the safety limit, the cut-off switches (one for 120V AC power, the other for the propane burner) will shut down the electrical and propane lines powering the water heater.
  • These cut-off switches can be reset by pushing a button on each – a simple task.

The most popular RV brands are Suburban and Atwood (owned by Dometic). Water capacity in RV water heater tanks is generally six, ten, or twelve gallons.

  • Suburban gas/electric water heater tanks are stainless steel with a ceramic lining. An anode rod (fondly referred to as a self-sacrificing anode rod) is installed inside the tank to absorb corrosive chemicals and prevent corrosion of the tank.
  • Atwood gas/electric water heater tanks are made from corrosion-resistant aluminum and do not have an anode rod.

Less popular in the RV plumbing world is the tankless on-demand propane-powered water heater, which heats only the water inside the pipes of the heater unit.

Even less common is the Motoraid method of heating water in an RV. Found most often in Winnebago Class A motorhomes, the Motoraid system runs coolant from the vehicle’s engine cooling system through a set of pipes that extend to the rear of the vehicle to heat the water heater and the air in the RV.

A safety reminder: The 120V electrical heating element in the water heater will burn out if the tank is empty. Ensure you fill the tank before turning on the 120V AC power to the water heater.

  • When hooked up to city water, your RV water heater will have a consistent and unlimited supply of water, which will prevent your water heater tank from running dry unexpectedly.
  • If you’re dry camping/boondocking, your water heater won’t have 120V AC power and will run on propane only, so there’s no risk of burning out the electric heating element.

How To Service An RV Hot Water Heater

Gas/electric RV water heaters need regular servicing to prevent premature failure and faulty performance. To remove debris, RV water heater tanks should be flushed every six months. Anode rods should be replaced annually, and gas burners should be cleaned and soot-free for optimum performance. 

If you’ve rocked in dismay at your kettle’s calcified heating element, imagine what the inside of a poorly maintained RV water heater will do to your sensibilities. Most RVs experience extreme fluctuations in temperature and weather conditions during their lifespan, and RV heating appliances take temperatures to the limit, which results in metal fatigue, rust, and corrosion.

Common RV water heater problems include:

  • Sediment buildup inside the water heater causes a hotspot to form at the bottom of the tank, resulting in lukewarm water and rapid rusting of the tank shell.
  • Sediment and debris can block the hot water outlet valve.
  • Soot clogging the propane burner orifice results in an inefficient flame and lukewarm water.
  • A corroded pressure relief valve causing water pressure to drop.
  • Again, a burned-out heating element is caused by switching on the electric circuit to the heater when the tank is empty.

Here’s a concise overview of how an RV water heater works and how to diagnose problems.

To keep your RV hot water tank in peak condition, implement a routine maintenance schedule. Use these tools and products to:

  1. Remove the anode rod from the drain plug with the pressure relief valve closed (this will prevent the water in the heater tank from gushing all over you).
  2. Open the pressure relief valve and allow the water to drain out of the water heater tank fully.
  3. Flush the RV hot water tank with a high-pressure RV wand until the water runs clear of debris.

  1. Replace the anode rod every twelve months.
  2. With compressed air and a wire brush, clear the propane burner of grit, soot and insects, and use alcohol to clean the orifice of the gas valve.
  3. Descale the electric heating element. Fill the water heater tank with a 50:50 white vinegar/water mixture (six gallons).
  4. Turn on the 120V element. Let the mixture to stand for at least 12 hours.
  5. Switch the element off.
  6. Drain and flush the tank.
  7. Fill the tank with freshwater if the RV is in use, or leave it empty if you’re winterizing the RV.

For the fine details on servicing your RV’s water heater yourself, consult your service/owner’s manual.


A reliable and plentiful supply of onboard hot water will make your RV trip a true home-from-home adventure. Open the inspection panel on your RV’s water heater service bay and get acquainted with your water heater make and model number.

Get a pair of safety gloves and the tools suggested above, and kick off your water heater maintenance routine with an anode rod inspection and thorough tank flush. Follow the pointers above, and your H2O hero will make sure you never end up in hot water without a water heater!

Good luck, and happy camping!

Check out our article on: RV Water Pump Keeps Running (How To Troubleshoot And Fix)

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