RV.Net Open Roads Forum: Help replacing old Atwood Water Heater with New Atwood

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Topic: Help replacing old Atwood Water Heater with New Atwood

Posted By: GlennLever on 07/11/15 02:14pm

Well I am trying to replace my old 10 gallon electric / gas Atwood water heater.

Water inlet and out let appear to be in the same location.

110 volt line hook up is in the same location.

The old unit has three wires from the control unit (Blue, Green, Brown)

The new unit has four Blue, Green, Orange, White)

It appears that the old unit used brown to trigger gas in the hot water heater, and the 110 was turned on manually either by a switch on the back of the unit or in my case a manual separate switch in the bathroom.

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The new unit appears to have a separate line for gas and electric and the white (for electric) troughs a relay on the back of the unit for electric.

There appears to be a way to use the same single switch I currently have by tying the orange and white together.

The new instruction are really bad.

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Has anyone run across this?

What I think I do is use the single switch and than if I also want electric I use the switch in the bathroom to supply 110 to the relay which will be thrown because the "Atwood switch is already on???

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Posted By: Tom N on 07/11/15 04:41pm

Have you thought about going to a new instantaneous on demand tankless water heater?? That's what I would do.

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Sarver, PA/Crystal River, FL/Shelocta, PA · W3TLN · FMCA 335149 · Mystic Knights of the Sea
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Posted By: Old-Biscuit on 07/11/15 05:06pm

Your problem(s) are that you have a 1997 model WH and trying to replace it with a 2014 model.

They are NOT the same.
Atwood changed designs in 2004.

Previous used 120V AC directly to electric element via On/Off switch and set of t-stats on backside of WH tank.

The design change uses 12V DC for electric & propane operation via relay, a circuit board and 1 set of t-stats for both heat sources.

You will need a DC fused wire to a new ON/OFF switch (Dual switch with fault light is better change out than 2 separate switches)

Then that electric On/Off (White wire) thru circuit board will power a relay that is in electric cover on back of WH tank where element is. Relay triggers 120V AC to element

Propane is from DC fused wire to On/Off switch then thru circuit board (orange wire).

Blue wire is DC from circuit board to Fault Light in On/Off panel

Green is 12V DC (-)

New Dual On/Off Switch
New DC wire run for electric (white)

Old 120V AC wire to element
Old Brown wire for propane (orange)
Old Blue wire for Fault Light

Is it time for your medication or mine?

2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31

Posted By: GlennLever on 07/11/15 05:09pm

Tom N wrote:

Have you thought about going to a new instantaneous on demand tankless water heater?? That's what I would do.

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Did not want to change all the wiring and plumbing. Looks like I will have to change some wiring, and with the ridge insulation on the new unit the plumbing does not fit.

I think I will grind the insulation so the plumbing does fit.

I did go to home depot and get fitting to space it out, but that would put a strain on the piping. So the insulation will get removed, and than I will pack fiberglass insulation back in. That is what is on the original.

Posted By: GlennLever on 07/11/15 07:39pm

Old-Biscuit wrote:

Ok, so if I tie the orange and white together, and retain the old 110 volt wall switch switch....when the 110 volt wall switch is off even though the 12 volt relay has turned the 110 on, on the heater the heater will still only run on propane because there is no 110 supplied to the heater (wall switch is off).

If I turn the 110 wall switch on then the heater will run on both propane and electric for quick heat up (instruction manual says this is ok, circled in red)

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The only down side is I cannot operate the water heater in just the electric mode with out adding a second switch. I cannot think of a time when I would want to do that, but my rewire in the further to be able to do that. I am currently in a time crunch as I am leaving for Norwalk this Wednesday and need to be done by then.

When I placed the order with American Coach they assured me that there were no retro fits necessary to install the heater.

There is this change to the electrical system.

The box that holds the relay for the electric operation which is on the back side of the heater is directly in the path of the plumbing (I have a solution and will post it when complete).

The tank is now insulated with foam rather than fiberglass mat which sticks out further and obstructs the outlet pipe. A little grinding to dimple the foam solved this problem.

Posted By: Old-Biscuit on 07/11/15 10:42pm

NO you do not want to tie the white and orange together.

Yes...you can turn both electric and propane on at same time for faster recovery.
ANY water heater with both electric/propane can do this.

Yes......this water heater is a replacement for your old water heater in that it is a combo (electric/gas) and will fit in same opening.
But it does require new wiring scheme due to design changes.

120V AC needs to be wired to/thru the box with relay. Relay is DC activated which allows AC to element when a 12V DC ON/OFF Switch for electric is turned ON

Propane uses 12 DC and will light off when a separate 12V DC ON/OFF switch is turned ON

BOTH electric and propane use 12V DC to/thru circuit board in order to function.

You could just wire propane circuit....all wiring is already there.
And deal with electric wiring when you have proper time to do it correctly.

Posted By: GlennLever on 07/12/15 06:18am

Old-Biscuit wrote:

Am I missing something?

The instructions for the new hot water heater (figure 10 single switch hookup) says that the orange and white wire goes to the same terminal>

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Posted By: Chris Bryant on 07/12/15 06:29am

You can do as you suggest- the only thing you will not be able to do is run the water heater on electric only- only gas, or gas/electric.
If it is going to be impossible to pull a new wire to the original switch, you could mount the new switch close to the water heater and feed it with the old line. Original switch would be a "master" (I would then wire the light to simply indicate "on").

-- Chris Bryant

Posted By: Old-Biscuit on 07/12/15 06:42am

That diagram is showing wiring for gas or electric with one switch.....

What is missing is that 2 switches are needed. One for each heating source.

Can you tie both to 1 single switch. Never tried it. Not a normal/standard configuration
Both electric/gas would operate ALL the time/at same time.
No individual heating option.
IF 'Fault' occurs don't know if both sources would trip or just one with issue ?
(Individual switches.......only the one with issue would trip on fault. Fault reset by turning On/OFF switch off then back on--after issue repaired that caused fault)

Posted By: GlennLever on 07/12/15 06:49am

Old-Biscuit wrote:

Instructions says that when operating both if the gas fails to light the fault light will not light and the unit will continue operation on just electric.

The old unit had a separate wall switch to supply 110 electric to the heater. If I use the same wire the new unit will not receive 110 unless the wall switch is turned one (even if the units relay for 110 is tripped by the single switch).

I think I'm good that way.

Now I just have to overcome the physical differences (location of the 110 relay box on the rear is in the way of the plumbing, and the ridge foam insulation on the back sticks out and interferes with the plumbing also

Posted By: Old-Biscuit on 07/12/15 07:16am

GlennLever wrote:

Go back an re-read that statement.
It is talking about a 'dual switch' panel with one fault light.
If both 'switches are on and gas faults......then light will NOT come on until electric is turned off.

Should NOT wire electric directly and use your old on/off switch.

With the design change.......only ONE set of t-stat (DC set) that are wired thru circuit board.

Old design had 120V AC set of t-stats for electric and a 12V DC set of t-stats for gas. Worked independent of each other.

New design....one set for both...using DC thru circuit board.
Running 120V AC directly to element bypasses DC set of t-stats.
NO temp control that way. Element would be ON----heating without control or trip scheme.

Posted By: GlennLever on 07/12/15 10:02am

Old-Biscuit wrote:

GlennLever wrote:

I think you are misunderstanding me.

I will wire 110 to the new unit as it was intended (allowing the 12 volt signal from the water heater control board to the relay to turn current 110 on / off to the heating element).

The original 110 wall switch was used to power the old water heater can than be used to interrupt the 110 even when the 12 relay on the back of the new water heater is on, this will allow the water heater to run on just propane.

The only option I will not have will be to run on just electric.

I will install the water heater so that I can install this option at a later date.

Posted By: Old-Biscuit on 07/12/15 03:12pm

GlennLever wrote:

Old-Biscuit wrote:

GlennLever wrote:

That should work.

You will have the electric DC circuit 'hot' anytime you turn gas Switch On.......might want to make a notation in outside compartment to that affect

Boy I'm glad we worked thru that [emoticon]

Posted By: GlennLever on 07/12/15 03:37pm

Old-Biscuit wrote:

GlennLever wrote:

Old-Biscuit wrote:

GlennLever wrote:

Just test fired the water heater on propane, it fired up.

I shut it right back off.

Now just need to hook up the water lines.

Seal the unit to the motor home.

And fire it up for real and see if it heats water and shuts off.

Posted By: Old-Biscuit on 07/12/15 10:20pm

Normal t-stat is preset for 140*F
ECO t-stat (Hi temp) is preset for 180*F

Should take roughly 35-40 minutes to reach temp on cold tank

Posted By: GlennLever on 07/13/15 12:52am

Water Heater

I have been pledged with problems with the water heater since I purchased the Motor Home.

Back when I was having RV service centers working on the motor home I had Caledonia RV work on the water heater on three different occasions. It was never right.

On electric service the water only got luck warm (on one of the attempts by Caledonia RV the unit was removed and a new heating element installed. There is no access panel to do this with the unit installed). See pictures later in this story of the large access hole provided for service (I’m being sarcastic).

The other problem is quite strange. The heater worked fine on propane, but if it rained it would shut off. If you opened the cover nothing was wet inside. Once it stopped raining it would work fine again.

So…I decided to take a look, took the burner out.

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Burner look ok., just a little dirty.

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There was a large gap on the ignition points, and they were really dirty.

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Cleaned them up and reset the gap according to the instruction manual.

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Put it all back together.

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And fired it up. Adjusted the air shutter until I got yellow flame, and then backed off until it went away (per the manual) The unit used to “roar” but now it is quite, quite.

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Went on our trip to Bowling Green where we had quite a bit of rain and the water heater did it thing, stopped working while it was raining and worked fine when it was not.

Enough is enough, time for a new unit.

Ordered one through American Coach and to my surprise it was cheaper that what I could get it for through Amozon.com

The first unit came. Note, I said first unit.

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and it was damaged.

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I probably could have straightened it out, but you know what I’m paying close to $500.00 for this thing so I expect it to be in better condition. I called American Coach and sent them some pictures. They refunded my money and told me I could keep the unit. I ordered another one.

I met the UPS guy as he was walking it up the driveway, it was in better shape but still bent up.

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He noted it as damaged when delivered. I called American Coach and explained that it had been opened in the presence of the UPS guy and that this one was damaged also. I explained that I thought I could straighten it out and use it. The offered to reduce the price, but it I accepted I would not be able to return it if it failed to function after installed.

My wife was listening to the conversation and said I should get yet another one. American Coach agreed to ship another one over night at their expense, as the trip to Norwalk is now 5 days away.

The third one arrived and I was able to meet the UPS guy again in the driveway. The third one was worse than the first two! I refused the shipment and the UPS guy took it back with him.

Called American Coach and made an agreement to take the second one for $200.00 and accept the risk of it not working once installed, yeks.

Time to start the replacement.

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Off with the door. One of the things wrong with the first unit is it looked like it had been opened and things removed, one of the things missing was one of the hinges. The hinge that was there was installed. In the unit I am going to install both hinges were taped to the inside of the metal frame.

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I mentioned earlier that a large access hole was provided to work on the back side of the water heater, in this case I need to disconnect the piping so the unit can be removed.

This is that large access hole, it is located inside the closet, so even to get to it you have to be a contortionist. The image of me in the right side of the picture is actually a reflection of me in the mirror mounted on the closet door.

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And if I stick the camera inside the hole to show you the lines that need to be disconnected this is what you see.

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Let’s get this thing out. It appears that when the unit was removed by the RV Service center they sealed it back in with silicone.

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Man this is coming out hard, feels like it is stuck.

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I’m trying to be gentle because if the new unit does not work I will need to put this one back in. It seems awful heavy?

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I figured out why it was so heavy! Ten gallons of water weighs a lot!

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It’s out.

I removed all the old sealant and silicone. Time for a test fit.

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It is a tight fit. The upper and lower edges of the hole are framed in steel, the wall is two inches thick! The rigid foam insulation on the new unit has no give to it while the old unit was surrounded by fiberglass insulation. This will come back to haunt me later, read on.

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I cannot leave the hole this way so time to bring out the wire wheel and then some good old Rust-o-leum damp proof primer.

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I was reassured by American Coach that the new unit would not require any “Refittment”.

I found out that was not the case.

Here are the backs of both the new and old units. There are some differences here.

1) The new control panel on the back of the new unit sticks out to far and blocks the area where the inlet pipe needs to go.

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2) The new rigid foam is thicker than the old fiberglass and there is no room to screw the outlet pipe in the Motor Home onto the back of the water heater.

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3) Finally the control units are different.

This is the control unit in the old unit. Note that there are three wires existing the unit into the Motor Home.

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This is the control unit for the new unit. Note the number of wires leaving the control unit.

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Turns out they are NOT the same.

Atwood changed designs in 2004.

Previous units used 120V AC directly to electric element via On/Off switch and set of t-stats on backside of Water Tank.

The design change uses 12V DC for electric & propane operation via relay, a circuit board and 1 set of thermostats for both heat sources.

Water inlet and outlet appear to be in the same location, but there is a problem with them anyway, I will explain further down, first let’s talk about the electric.

110 volt line hook up is in the same location.

The old unit has three wires from the control unit (Blue, Green, and Brown).

The new unit has four (Blue, Green, Orange, White)

It appears that the old unit used brown to trigger gas in the hot water heater, and the 110 was turned on manually either by a switch on the back of the unit or in my case a manual separate switch in the bathroom.

[image]

The new unit has separate DC control wires for gas and electric the white (for electric) tells the control board you want the electric heating element to come on. The control board uses the same thermostat for both gas and electric operation, the control board uses a 12 volt DC signal to close a relay on the back of the unit to supply 110 to the heating element (the old unit uses a separate thermostat and no interaction with the gas control board).

So I have three fitment problems to contend with, let’s take them in order.

1)The first thing we need to contend with is the control unit being in the way of the inlet pipe in the Motor Home.

It has to be moved.

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What a mess inside, why would someone wire something like this? There is no insulation between the relay and the hot water tank. Everyone know heat is the enemy of electronics.

Let’s turn it around so that it is in the center of the tank. This will allow the inlet pipe in the motor home to pass underneath it. There is still the mater of no insulation between the relay and the hot water tank.

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Well not any more.

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Now let’s clean up the wiring. I will wire the 110 as the new unit was expecting, using the 12 volt DC signal from the front control board to turn on the electric heating element. I will retain the manual wall switch from the old unit. This will allow me to run the unit on just propane. I will explain this in more detail further down, keep reading.

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Might as well add some more insulation to the bottom of the tank where the control panel was originally mounted and this is what the back now looks like with the wiring redone and the added insulation. Note that the wires to the heating element come through a rubber grommet that was not there before and the 110 12 gauge supply wire now has a plug on the end so the unit can be removed easily from the Motor Home

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First problem solved.

2) The rigid foam does not allow me to connect the pipe in the motor home to the outlet on the heater.

My first thought for this problem and the problem of the control panel on the rear of the water heater was to space it out further so there was clearance.

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I could have done this, but decided that I would then have to change the piping in the motor home to match the change in spacing. If I did not do that than the pipes in the motor home would be under stress. Although they are plastic and would “bend” to meet the new spacing, my concern was they are “older” and might be acceptable to fatigue cracking if put under stress.

Then it dawned on me the problem was there was no room, so let’s make some, out came the grinder. Now we have lots of room.

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Problem two solved.

3) The old unit has three wires from the control unit (Blue, Green, and Brown). The new unit has four (Blue, Green, Orange, White).

There appears to be a way to use the same single switch I currently have by tying the orange and white together.

The new instructions are really bad.

[image]

So I think I got this straight now. If I tie the orange and white wires together, and retain the old 110 volt wall switch for the old unit....when the 110 volt wall switch is off, even though the 12 volt relay on the new unit has turned the 110 on, on the heater, the heater will still only run on propane because there is no 110 supplied to the heater (wall switch is off).

If I turn the 110 wall switch on then the heater will run on both propane and electric for quick heat up (instruction manual says this is ok, circled in red)

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Time to do some more wiring.

The new unit came with a female connector, but no male connector. I like weather pack connectors as you have seen in earlier wiring.

Off comes the Atwood connector

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to be replaced by a weather pack connector

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Now I still have four wires instead of the original three with the old unit. I want to install this unit so that if in the further I want to have separate control over the heat sources (remember I can heat with just propane, and I can heat with both, but what I cannot do is heat with just electric, for the life of me I cannot think why I would want to do that).

What I did was jumper the white and orange (gas and electric) together on the motor home side of the weather pack connector. I ran the jumper into the motor home and it can be accessed through my large access hole in the closet.

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I will coil this up and wire tie it inside the water heater compartment for later contemplation.

So now I think we are ready to connect the unit and put it in place. Note that both the 12 volt DC signal wires and the 110 power is a quick connection.

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The unit is slid into the hole.

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One finial struggle. The grommet that goes around the gas line. The hole in the grommet is a ¼ hole for the gas line, but the end of the gas line has the connector nut on it. What some past RV Service center did was cut the old one so that they could put it on. What I did was use two needle nose pliers to stretch the opening in the grommet open far enough to slide over the connector nut.

This effort did not go unrewarded. In one of many attempts one of the needle nose pliers slipped and hit me in the chin and I now have a badge of honor for my efforts.

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Now I have to use the large access hole to connect up the pipes in the motor home to the hot water heater.

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Everything fit! I filled the freshwater tank with water, and ran the onboard pump to fill the hot water tank. No leaks. I hooked up city water from my house (more pressure). No leaks.

I fired up the range to purge the air out of the propane system.

I turn the hot water heater on . . . nothing happened.

I tried it again and it fired up. There was air in the lines between the range and the hot water tank. What a relief!

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The orange you see in the flame are the igniter points glowing red hot. I did adjust the air mixture.

The unit is very quiet, it brought the water up to temperature and shut off. I ran the hot water and the unit came back on to heat the water again.

I believe we have a success.

Tomorrow, rather today, I will have to drain the tank and seal the unit to the motor home. I purchased stainless steel screws and butyl tape to do that.

Every screw inside the steel frame was loose. I am not impressed by the quality control of Atwood. I believe all the damaged units I received were damaged due to very poor packing.

This novel is ended.

Follow my projects here.

Posted By: Chris Bryant on 07/13/15 06:07am

I really would not leave the element exposed on the back- any connection like this needs to be in a flame resistant enclosure, and I have seen many water heaters smoke the wiring at the element, plus the possibility of someone reaching blindly through the access hole and getting shocked.
There is plenty of flex in that pipe to add a longer nipple at the tank.

Posted By: GlennLever on 07/13/15 07:00am

Chris Bryant wrote:

The box that Atwood had over the element on the new unit was plastic, on the old unit was metal. I will cover the element with the old metal box.

I have to drain it today so I can move it to seal the outer lip and will add the box when I do that.

Posted By: Old-Biscuit on 07/13/15 11:21am

Glenn,

Heck of a change out.........most would have given up

You recognized the issues, found a solution and made it work

VERY nice write up and pictures.

I apologize for 'questioning you'...just playing 'devils advocate'.
Didn't want you to be wiring it up w/o bypassing safety controls.

Good job!!!

Posted By: GlennLever on 07/13/15 01:38pm

Ok...Almost the finial chapter in the water heater install.

I left the heater on over night with the internal pump on to keep the pressure up. No Leaks!

This time I was smart and drained the tank before trying to move it.

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Once drain I pulled the unit out far enough so I could apply butyl tape to the back side of the flange.

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I started in the middle at the bottom and went all the way around the unit with one piece.

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This was a fresh roll and working with it compared to my experience with the refrigerator was a dream.

I attempted to use the original holes but the flange holes did not line up with the holes in the motor home.

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I probably could have made them work, but I drill new holes so the screws would go in straight. I replaced the original self tapping screws with stainless steel screws.

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One drill to drill the holes and the other to screw the screws in.

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I trimmed off the excess butyl that was squeezed out leaving about 1/8 excess still sticking out.

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I used my fingers and squished the excess into a semicircle so water would not sit on the edge of the sealant.

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All of this including the silicone that I could not get off that was applied by a RV Service Center is hidden behind the cover.

Speaking of the cover, there is what appears to be a view port in it. It has always bothered me that it was opaque.

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Time to do something about it.

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I cut it out and epoxied a small piece of Plexiglas over the hole from the inside.

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I do not know what it's purpose is but now it is clear.

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So when install what you see is the bolt that hold the air color on the gas valve in place.

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Anyone know why this is here?

The inside hatch cover is put back in place.

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Finished, right?

Well after several heating cycles the pressure relief valve has started to drip when the temperature of the water gets close to the high point. If I relieve the pressure by turning a hot water valve on the dripping stops.

My old tank used to do this. I replaced the pressure relieve valve on that unit and it still did it.

I have had a conversation with several people and they tell me this is a common problem,. That these hot water heaters heat the water hot as there is limited quantities of the hot water. That means you can mix more cold water with it and the hot water lasts longer.

Do you have this problem.

I am thinking of installing a drain hose from the valve through the coach and to the bottom of the coach just as the defrost from the refrigerator does.

Posted By: Old-Biscuit on 07/13/15 03:39pm

Due to closed system and higher normal temp t-stats weeping can occur when air gap is not present.

Air gap allows for swelling of water when heated and absorbs increase in pressure

Turn off water supply
Open faucet hotside to relieve pressure
Open T&P Relief Valve with lever,,,,,,,,,,when water stops flowing out let it snap closed
Turn on water supply close faucet

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Posted By: GlennLever on 07/21/15 06:48pm

Traveled for 5 days this past week and the water heater worked flawlessly even through heavy rain.

I did try putting the air pocket in the tank, did not change the drip.

Posted By: getaround2it on 09/20/15 01:55pm

GlennLever, excellent post here and exactly the topic that I was looking for. [emoticon]

What became of getting your "electric only" function resolved for your water heater?

I fulltime in my 2002 Winnebago and stay on my sons property. I don't take the motorhome out very often for the time being and I don't want to deplete my propane on hot water when I am plugged into 30 amp 120v full time. I want to keep my propane available for cooking only. I heat the coach with 120v when needed too.

So I want to use my new replacement 4E water heater on electric only. This will allow me fewer trips to have my propane tank refilled and also prevent me from having to buy into the "stay awhile" portable tank propane source should my builtin tank run empty at a time I don't want to move/drive to a refill point.

I'm parked and set up on a slope requiring lots of levelling blocks and it's not so easy to just raise the jacks and go.

I also wish to keep my existing switches functional and avoid installing the new dual switch the new water heater came with which would have to be installed on my water control panel inside the basement compartment next to the water heater compartment.

Have you found a way to separate your white and orange wires to gain the "electric only" feature by utilizing your existing indoor coach switches?

As I search the web for answers I have found one forum member on a different board that had a tech accomplish this on a similar Winnebago but the owner has no idea how the tech actually wired it. [emoticon]

So currently I have not wired my water heater yet.

Posted By: Chris Bryant on 09/20/15 03:10pm

getaround2it wrote:

What became of getting your "electric only" function resolved for your water heater?
...
Have you found a way to separate your white and orange wires to gain the "electric only" feature by utilizing your existing indoor coach switches?

Simply hook the white "electric" wire directly to a 12 volt source- you will have to find power close to the heater to avoid running an extra wire.
This is about the only way to do it, as the heater uses the single thermostat and a relay, which must be used.

Posted By: GlennLever on 09/20/15 05:01pm

getaround2it wrote:

GlennLever, excellent post here and exactly the topic that I was looking for. [emoticon]

So currently I have not wired my water heater yet.

Ok...

Instructions says that when operating both if the gas fails to light the fault light will not light and the unit will continue operation on just electric.

So...
If you tie both wires together, turn the gas valve off, the heater should work on just electric.

Failing that, just hook up the electric wire to your single switch and the unit should only want to work of electric.

Posted By: Bird Freak on 09/20/15 05:22pm

Great job!

Eddie
03 Fleetwood Pride, 36-5L
04 Ford F-250 Superduty
15K Pullrite Superglide
Old coach 04 Pace Arrow 37C with brakes sometimes.
Owner- The Toy Shop-
Auto Restoration and Customs 32 years. Retired by a stroke!
We love 56 T-Birds

Posted By: getaround2it on 09/23/15 11:56pm

OK got it.

Here is what I ended up with:

Blue wire to blue wire.

Green wire to green wire.

Orange wire to brown wire.

New 12v. wire from the house battery to the white wire.

Results:

The original brown wall switch turns the water heater on with 110v. electric only.

The original low voltage switch on the monitor panel turns the water heater on with LP only.

To provide both LP & electric turn both switches on.

I have no idea why Atwood can't outline this procedure and include it with these new 4E water heaters for those of us replacing an old model 3E and would like to keep using the original switches inside the coach.

Note:

Where you connect your 12v. wire powering up the new heaters' white wire is up to you. It has to be a full time on source which is actually keeping your new 110v. relay at the rear end of your new water heater "live". Keep in mind if you grab the 12v. off a house battery and you store your rig for a spell with no connection to power, this 12v. wire to the relay will eventually draw your batteries down.

For my needs, I didn't want to start poking my wiring harnesses near the water heater compartment to find a 12v. source that would always remain hot. Because my battery box in under my entry stairs right next to the water heater I opted to take my power directly off one house battery and I added an inline fuse just to be safe and added a switch next to the water heater that shuts off this 12.v source to the heaters' white wire should I store the motorhome for a while. Just as I would use my battery disconnect switch when storing the motorhome I have one more checklist item............turn off the water heater switch in the basement.

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