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RV Water Heater Basics, Old And New

Most modern RV water heaters (WH) operate in either Electric or Liquid Propane (LP) Gas mode.

In entry level RVs though, the water heater may only operate in LP gas mode.

Water heaters in other motorhomes might operate by a third heating method called Motoraid (see more below), which uses waste heat from the motorhome engine to heat the water as you drive.

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Finally, some high-end RVs may have an entirely different system in which the water heater is part of a diesel and electric central heating system, typically either the Aquahot or Hydrohot brand names.

RV Water Heater Basics, Types, and Maintenance

Standard RV Water Heater Basics

The standard RV water heater sizes are 6 gallon or 10 gallon—much smaller than a residential heater.

If you’re new to RVing, you may find that you’re not be able to enjoy quite as long a hot shower as at home. A few models are advertised as being 16-gallon heaters, but these are actually 10-gallon heaters that superheat the water and then mix cold water at the outlet, making them roughly equivalent to having a 16-gallon heater at the usual 140 degrees.

There will be separate On/Off switches for the Electric and LP Gas Modes. The RV water heater can be operated in either mode or both can be used to speed up the heating process.

Both are controlled by a thermostat, so the heater only runs as needed.

In LP gas mode, a heater control circuit board insures safe operation, so 12v power is needed for it to operate.

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Most water heaters have separate thermostats for Electric and LP Gas modes and the two modes are pretty much independent of each other.

If one doesn’t work for some reason, usually the other will still be functional.

The standard thermostats are fixed temperature, typically 140 degrees in recent models, and you can’t adjust them.

However, there may be adjustable replacement thermostats available for some brands & models.

RV Water Heater: Electric Mode

An RV water heater in Electric Mode can be used whenever you have 120v shore or generator power available.

It requires a fairly substantial amount of electricity, about 12 amps (1400 watts), so you may not want to utilize it if power is limited, or if you want to run other high-power appliances (like an air conditioner or microwave oven) at the same time.

This is primarily a concern in RVs that have only 30A shore power wiring, or any time the RV is plugged into an outlet that has 30A or less available.

You can switch it off temporarily (the water will stay hot for some time) or change over to LP Gas mode.

When you switch on the Electric mode on your RV water heater, the Electric Mode thermostat controls whether 120v power flows to the electric heater element or not.

The heater element cycles on & off as needed, heating the water, just like your home water heater. There is no need to turn the heater off when not in use.

RV Water Heater: LP Gas Mode

The most basic model gas RV water heater has a pilot light which must be lit manually with a match or sparking device.

There is a manual valve that must be set to the “Pilot” position to light the pilot and then you move the valve to a Run position for continued operation.

Once the pilot light is lit and the heater control circuit board detects a flame at the flame sensor, the gas mode thermostat starts and stops the flow of LP gas to the burner, where it is ignited by the pilot flame.

There is no need to relight the pilot each time more hot water is needed.

If the pilot goes out, no flame is detected and no gas is allowed to flow, preventing any danger from leaking LP gas. When you no longer need to have hot water available, turn the Pilot Control switch to Off and the heater shuts down.

Most modern RV water heaters are the DSI (Direct Spark Ignition) type, which has no pilot light. When you switch on the water heater in LP Gas mode, the gas mode thermostat will call for it to be heated as needed.

When heating is called for, the heater control circuit board opens the gas valve and activates the igniter, making a spark at the front of the heater’s gas burner tube, and (hopefully) igniting the flame.

At the same time, the control board starts sensing for a flame (the igniter doubles as a flame sensor). When the burner flame is sensed, the ignition sequence is complete.

If no flame is detected after a preset time (about 15 seconds), the gas valve is closed, the igniter is turned off, and the system “locks out,” meaning it won’t allow another attempt at restarting until the system is reset by turning it off and on again.

Usually a red indicator light will show at the LP Gas Mode switch if the heater fails to light when needed.

While you can run a DSI RV water heater in LP Gas Mode while driving, this is generally not necessary since it heats up within 20-30 minutes after it is turned on anyway.

A Manual Pilot type of water heater usually does not work while driving—the wind blows the pilot light out. Few RVers leave their water heater on while traveling—it’s just a waste of fuel.

Truma Hot Water Heater. Photo via iRV2 Forums
Truma Hot Water Heater. Photo via iRV2 Forums
MotorAid

The MotorAid system is conceptually quite simple.

Water from the motorhome’s engine cooling system is circulated through tubes embedded in the water heater. Whenever the engine is at its normal operating temperature, the water in the tank is being heated by the waste heat from the engine.

This provides heated water as well as assisting in cooling the engine.

RV Water Heater Maintenance

Your RV water heater requires very little care in normal use.

The Electric Mode is essentially maintenance-free, and the LP Gas mode needs only an annual cleaning of the burner tube to remove rust flakes, spider webs, etc.

A vacuum cleaner nozzle on the tube is usually sufficient. However, when you store the RV for long periods you should drain the tank (see your water heater’s owners manual) and, if sub-freezing weather is expected, winterize the associated water lines.

The RV’s heater plumbing usually has a bypass valve to assist in winterizing.

The heater bypass and winterizing procedures are part of the general RV maintenance information and not covered in the WH manual.

Endless Hot Water Heaters

Endless hot water heaters that run on your RV’s fuel supply are rapidly growing in popularity as the vendor landscape changes and the demand increases. Units from AquaHot, Truma, & Girard offer an endless supply of hot water, either through a tankless or hybrid solution.

As long as you have water and fuel (Gasoline or Diesel), you can have hot water. These types of water heaters are proving to be reliable, and are definitely the future for hot water solutions in today’s modern RVs.

Many of these require an annual maintenance procedure. Fuel nozzles need to be replaced, burner drums cleaned, and heating fluid changed. Failure to keep these maintained will result in poor or failed performance and cold showers.

Keep track of all your water heater maintenance, regardless of which type you use, with an online tool such as RV LIFE Maintenance. Not only can you keep all your maintenance records and documents in one place, you’ll receive timely reminders via email when maintenance is due, and potentially avoid a costly repair due to lack of maintenance.

Whether you have a small camper or large class A motorhome, RV LIFE Maintenance can keep track of it all. Keeping accurate maintenance records also increases your resale value, should you ever decide to do so.

See more about general RV winterizing.

See more about RV water heater repair.




56 thoughts on “RV Water Heater Basics, Old And New”

  1. I have a suburban water heater. Its heating fine but when I turn on faucets for hot water it comes out good at first then it starts losing pressure but stays hot. Doesn’t matter if it is kitchen or bathroom faucets. I have a 2006 forest river travel trailer park model. Do I have sediment in my lines? I have changed anode and drained and flushed out tank with pressure end for the tank. I’m going nuts and I don’t know what to do. I’m new to rv living and don’t know what to do about this problem.
    Can anyone explain how to troubleshoot and fix my Delima in detail ? I live full time in rv park. I’m disabled and on limited income and would like to fix myself if possible. Thanks for your time and information.

  2. I have a 6 gallon water heater that only allows a five minute warm shower. What options do I have to enjoy longer showers. Is a hott rod an option? We are full timers. Responses would be well appreciated.

  3. My water heater has the electronic pilot light. Up until last time it worked fine with red indicator light on inside stayed on while heater is on until I turned it off. Now when I flip switch on, indicator light comes on until it lights then indicator light goes off but heater stays on. Not sure if it will shut off when water gets hot, afraid to leave it on since the light inside is not staying on like it used too. Any info?????

  4. I have a 6 gallon suburban water heater a/c and propane, and it might be running at 90 degrees max on a/c. I opened the housing to find no discernible adjustment for temp. Can anyone help me out. It is on a 2015 Rockwood and is brand new but I am no newbie…6th camper and still trying to unravel the mysteries of this one!

  5. We just bought a new 6.5 gal electric water heater got it hooked up and water going into the tank but when we turn on the faucet no water is coming out could you please help?

  6. SO we are new to the RV world. Just bought our 1st rig. 1998 Thor Fifth Ave. Nice little rig. There are 2 problems though with it. The hot water quit working on the previous owner at the end of last season. He wasnt sure what happened. Is there anything I can do trouble shoot it? Model # on the heater is GC10A-3E. Any thought on what I can do? Thanks in advance for the help and looking forward to many years of Rv’ing!

    Daron

  7. My hot water tank pumps hot water for about 5 seconds then the water gets very cold, then it goes back to hot, and back to cold and so on. The tank is full of water, the flame in the heater is working. Any guess as to what might be causing the water to oscilate between hot and cold? thanks!

  8. I don’t see any mention of tankless water heaters. They seem like a good way to go as they can provide continuous hot water. They should use less propane because they only heat when there is demand unlike one with a tank. Are there any disadvantages?

  9. I have a atwood 10 gal (dsi) water heater in my rv. The heater does not lite. I have checked the gas valve, the ignitor by jumping them and they seam to work. the circuit board does not send a signal out for the heater to come on. Yet when I check the circuit board with a meter it seams to ohm out. What do you think it might be? also check therma cut off, it ohms out too. Thanks, Gary

  10. I am new at RVing. Have an Atwood water heater. Drained it as instructed for the winter. The drain plug is plastic. Looks as if it has plumbers putty on it. Cannot find anything that says to put new putty on it. Can I use teflon tape? Or do I need to put new putty back on it? Thank you for any advice.

  11. I have the Atwood GC10A-4E water heater in my motorhome. A couple things happen: In Electric mode, the water heater heats and then the Overpressure valve starts to leak and then the DSI light comes on. The gas mode does the same. My question is, can the ECO and thermostat be reversed on installation maybe causing the the water to heat to high? I removed the thermostats and noticed one marked as 60 degrees C and the other marked 65 degrees C? Installation instructions with the new thermostats don’t say anything about not switching them.

  12. I have a 99 catalinea coachmen. When I purchased my trailer the water heater wasn’t winterize and destroyed the heater. It was propane and electric. Is it possible to install a 6 gal heater that I purchased from sears? If so how do I figure out the wiring? Any ideas would help

    Thanks
    Ann

  13. I just bought a water hearer from a friend for my travel trailer and there are 4 ignition wires on this one, but only 2 wires coming out of my wall. Will I be able to use this new one or not? If so how do I hook it up. I would appreciate any information you can give me because I know nothing about these things.
    Thank you.

  14. We have a Salem 5th wheel. We went camping this week and when we ran water out of the hot water it smelled really strong of sulfur. We could not stand the smell and came home early. The tanks has always been drained each time we use it. What can we do to get rid of the smell?

  15. Look behind the waterheater and you’re going to find winterizing valves. One of these valves (3) has been moved allowing the cold and hot to mix. Top and Lower valve should be Open. The valve in the middle should be closed. I think you’ll find the middle valve was wrong.
    If you have a single lever style By-Pass be sure its in the correct position (it is marked). Hope this does it for you.

  16. I have a suburban hot water heater that is doing the same thing if you find an answer can you forward it to me. I try to trouble shoot my own problems but having no luck here

  17. I have a 1999 Fleetwood Mallard hot water heated via LP. We sustained a cracked water tank due to improper winterizing. I will be removing tank and will have it repaired. There is a two way valve system on the unit therefore when tank removed I can still have water to my trailer but not hot water. Now the propane connection will need to be capped during repair , can anyone tell me what size of propane connection?

    Thank you in advance

  18. Did you ever get a resolution to your problem? I have an Atwood 6 gal. heater and it does the same thing. When using water from the holding tank, hot water runs until the pump turns on, then the water is cold. The only thing that could cause this is the cold water intake pipe,, which usually runs to the bottom of the tank so the hot water stays on the top of the tank and is used first. If this is broken off, just as soon as cold water enters the tank is short circuits to the hot water outlet (at least this is what happens on a household hot water heater). I can’t find any parts list which states that this pipe can be replaced which is possible on household HW heaters. Can’t find anybody but you that has run into this problem. Any advice???

  19. It’s your valve located in the hot water area probably running the water to hot is a blow off valve instead of damage the tank run it how it was that day and watch it drip out of that drain valve

  20. I have a 98 coachman camper with a atwood water heater. I’ve been having trouble with it so ive replaced the thermostat and eco switch, which didnt fix it. It seems to work fine if i leave the door open on the front of the water heater, once i close it, about a minute later it turns off trys to light then shuts back off and turns the red light on at switch. I’ve tried to adjust the air mixture tube but hasnt changed a thing. Any ideas?

  21. I have a Atwood? water heater in my RV, run on propane or 120. Model SW12DE and the SERIAL #111706648.
    Its a 12gal, 12000BTU.
    While camping this weekend I noticed a leak under the camper, that was under the water heater. I turned the supply off to the water heater and waited until it stopped leaking, and the parking pad dried. I opened up the panel behind the water heater that is in the basement compartment to check for leaks. NO leaks around the supply lines. I assumed the tank was empty since the water stopped leaking. Today I opened up the drain to the water heater and it seemed to be full. about 12 gals drained out. I was sure that it would be empty, and the tank would be bad. Any ideas???

  22. My hot water heater in my camper is hot but when I turn on hot water on it runs for a few seconds hot then it turns cold. I have both propane and electric. Doesn’t matter wheich is on.

  23. Where does the water run out? That shouldn’t happen, regardless of the position of the winterizing bypass valves.

    The tank has a drain plug at the bottom that should be installed, and there is a Pressure-Temperature (PT) relief valve nearer the top that may be manually open or just plain leaking.If that’s the water leak, fFlip the lever that opens/closes the PT valve and see if that stops it.

    If you have two valves in the bypass system, then having both turned to the right (crosswise to the pipe) would usually be the bypass position, meaning water does not go through the tank. However, handle positions are not standard and different brands of valves may have different open/closed positions, so I can’t be absolutely sure of that.

  24. i have a 1977 winnebago and when i am hooked up to water and turn the water on at the faucet the water just comes out of the hot water heater i don’t need the hot water at the moment but would like to have the water hooked up. i checked the valves and they are both turned to the right on the inside that would mean that the valves are off correct? should i try to turn them to the left to see if that turns them off or will that cause the water to leak on the inside of the RV where the valves are?

  25. Hi Robert,

    That is a tough one. After all the trouble and price to find parts it may be cheaper to get a new water heater. Best bet is to contact American Water Heater Company and request technical assistance to see if they can offer direction on where to find parts. They own the Mor-Flo brand. Good Luck!

  26. Have an older Mo-Flo water heater in a 76 e350 motor home. Need a new gas control /pilot light/thermostat assembly. Any idea where to get. Have serial number off heater but cannot find model anywhere!

  27. There is no standard location – RV manufacturers put them wherever it is convenient for manufacturing. Suburban brand heaters may have the electric switch right on the tank itself.

    Also, there isn’t a “change” switch. There will be an On/Off switch for electric heat and another switch for gas heat and they can be used individually or both turned on at the same time. Using both heats water faster. The two switches may be in different locations.

  28. In that model & year of coach, the water heater electric switch is typically inside the cabinet under the bathroom sink. It may not be easy to see even with the cabinet doors open.

    On my 2004 American Tradition I added a new switch (with an indicator) on the surface of the cabinet.

  29. I would turn off the circuit breaker for the water heater rather than relying on the heater switch alone. That way you can be assured there is no 120v power to the heater.

  30. today I had called an RV repair man to come look at my water tank that I believed to be leaking. When I got home after he had been here checking things the area with please heater was scorched and burning up the side of the camper and you could see the heat fumes coming off. I immediately unplugged the electrical to the camper and my question is once I turned off the hot water heater switch on the inside. Is it still safe to turn the rest of the electrical on without worrying about any issues.

  31. Rick,

    We have never worked in an American Tradition so cant tell you specifically where you may find it. Hopefully one of our readers will offer some help who has one!

  32. If you have hooked up the water to your RV at the park, that is all that is required to run the water heater. The holding tank only needs to be filled if you dont have a line connected, in which case you need to turn on your water pump.

  33. I have water into RV from an outside line. Do I still need to fill the holding tank before turning on the water heater? I’m hooked up already at an RV park.

  34. I have a 2005 American Tradition. I cannot find the switch that moves the hot water tank from propane to switch to electric.. Any help would be great,thanks

  35. I prefer Atwood heaters, but Suburban makes a good unit too. Functionally and quality wise they are essentially the same, but the Atwoods don’t require periodic replacement of an anode rod like the Suburbans, so that is a plus factor for me.

  36. Another possibility that occurs to me is that your heater bypass valve is leaking and letting cold water mix with the hot. This can happen if the valve(s) isn’t fully seated in the normal use position, or if the valve itself has failed and leaking internally. There are several different heater bypass designs, using one, two or three valves, so I can’t give more details on how to check that. Try changing the position of whatever valves you have and then moving them back to the normal use position. Sometimes that’s enough to re-seat them so they work properly.

  37. Try it in LP gas mode and see if it gets hotter. If it does, there may be a problem with the electric heater element itself. It can be replaced fairly easily and you can probably find a compatible one at a home center. Another possibility for an electric heat only problem is corrosion on the 120v power wire, either at the heater connection or at the circuit breaker in the load center.

    If LP gas mode also fails to reach 140, the problem is either in the thermostat or the controller. Even a working thermostat might not produce the right temperature if it is not hedf firmly against the tank wall so it can read temperature accurately.

  38. If your water heater has a single valve bypass system (instead of the traditional 3 valve type), it has a check valve where the hot water line exits from the tank. Those check valves can get clogged and stop the flow of hot water.

  39. My water heater is not heating the water like it used to. I have changed the circuit board, thermostat and eco sensors, and the thermal couple wire. On electric mode it used to heat to 140 degrees now it gets to about 110 or less. And it takes a long time to get there. What else can I check.

  40. Look behind your hot water heater there should be a in line check valve. It lets hot water out and stops it from going the other way. Check to see if it may be stuck. There is also a screen in the exit line at the tank you can check and see if that is plugged . If that does not work follow the line from your sink to the hot water heater and look for a shut off that may have been tripped or perhaps something has damaged or crimped the line. It is possible it may need to be replaced if that is the case.

  41. My water heater heats but no water is coming out of the faucet. I checked and there is hot water in the tank. What is keeping the water from going to the faucet? None of the valves have been changed and it was working yesterday.

  42. I have an Atwood 6 gal lo heater. It works fine and heats extremely well but once the water gets hot and it cuts off, sometimes it does not automatically come back on. I have to manually cut it off and back on.

  43. The air density decreases substantially at that altitude, so it may be necessary to adjust the air shutter (on the tube that feeds the burner) to better tune the air/fuel ratio.  The color of the burner flame is your guide to doing that – it should be all or nearly all blue. With the burner operating, open or close the air shutter to minimize the yellow and that may fix your problem.
     —–
    Gary

  44. My gas hot water heat in my RV works fine until we camp at higher altitudes 8,500 ft. It will light but after a short time it starts to “blubber” goes out and restarts multiple times. Does ayone one have suggestions.

  45. Try pulling the pressure relief valve on your hot water heater if water comes out like a water faucet then water is reaching your hot water heater. If not then if your heater runs on propane light the pilot it should heat up. If it is electric heater make sure it is getting electrical power. You could send us some pictures of the heater we may be able to help you more.

  46. I got my heater to come on but I still don’t think its filling up the water heater tank. Is there anyway I can check to see if the tank is even being filled.

  47. I have a 86 companion. I don’t think my water heater is working. I have it connected with a hose continually but I don’t think it is filling up any tanks. Do I need to fill my tank on the other side of the trailer

  48. I have a 2013 Newmar Canyon Star. We were going out of town for 2 weeks and I turned the water off, but forgot to turn the hot water heater off. Will it be okay?

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