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Old 03-10-2015, 03:12 AM   #1
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THOR #1393
2015 ACE 27.1 Water Heater

Can anyone think of a reason not to replace the plastic drain plug on my water heater with a brass plug? The first time I tried to drain the water heater, the plastic plug began striping and I discovered that my boat's brass plug was a perfect fit. I wrapped a little Teflon tape, reinstalled and have had no issues. Just wondering about using brass on the metal threaded drain hole or some other reason why the manufacturer used a cheap plug instead of a quality one.. Thanks.
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Old 03-10-2015, 03:22 AM   #2
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THOR #121
Water heater is made out of Aluminum and the brass plug is made out of brass. A goog chance of Electralisis being created
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Old 03-10-2015, 03:50 AM   #3
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They use a non-metalic plug to protect the tank.

As fhenn indicated - anytime two dissimilar metals are in contact with each other in the presence of water, galvanic current occurs.

I am going to fall back my previous experience with boats on this. Boaters have to contend with serious galvanic corrosion issues, so I picked up a bit of "horse-sense" along the way when I had boats.

Galvanic current will corrode the less noble metal. Aluminum is less noble than brass, so if you use a brass plug, the tank will be more prone to corrosion. The amount of corrosion depends on the two metals, the distance they are apart on the Nobility Scale, their surface area, the conductivity of water (due to dissolved mineral content), and so on.

If you want to replace the plug with a metal one, then you should replace it with an aluminum plug, or with one having a sacrificial anode. Even if the aluminum plug may be a different alloy, it's position on the Nobility Scale vs. the tank's aluminum should not be significant, and thus will not likely cause significant corrosion.

I know some will say that Atwood heaters do not require anodes, but the heater has a brass overpressure valve, and assuming that is in contact with the aluminum tank, then some corrosion is occurring anyway. The corrosion rate will not likely be high because the surface area of the tank is much larger than the brass valve, but it will occur over the lifetime of the tank.

This topic is piquing my curiosity - I should measure between the overpressure valve and tank with an ohmmeter when I get my rig out of the snow bank and see if there is any continuity.

Atwood may not use an anode as they may feel the rate of corrosion due to the overpressure valve may not be significant. Or if there is electrical isolation between the overpressure valve and tank, corrosion will not likely occur; which is why I want to measure between the valve and tank with an ohmmeter. I want to see if there is any metal-to-metal contact.

But adding a brass plug increases the ratio of the brass to aluminum surface area, and if combined with the overpressure valve, perhaps to the point of having an issue.

Camco makes plugs for Atwood heaters that have magnesium anodes having 1/2NPT threads. If you buy one, make sure it is for an Atwood tank, as Suburban tanks I believe use 3/4NPT threads. Magnesium and zinc are less Noble than aluminum, so they will protect the tank (boat anodes are usually zinc or magnesium).

However, when using such anodes, a small amount of dissolved metal will be introduced into the water system since the dissolving anode will release metal into the water. Whether or not this increases the metallic content more than the typical dissolved metals already in the water I do not know.

So, I would recommend staying with the nylon plug and not worry about the small rate of corrosion that may occur in the tank due to the brass overpressure valve. But if you want to replace the plug with a metal one, use an aluminum one, with or without an anode (the Camco anode plugs for Atwood tanks are aluminum).

I would avoid using a brass plug.

Sorry for the long post...
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Old 03-11-2015, 02:52 AM   #4
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Thanks for the replies, very informative.. think I'll go back to the plastic plug..
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Old 03-12-2015, 01:41 AM   #5
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FW28z,


I went to an RV store today to purchase the replacement plastic plugs. I was told that Atwood water heaters already have an anode, which should be replaced yearly, and was shown one. They also sell brass plugs (with a drain valve in the center) and stated their use is fine as the heater has an anode. I didn't get a chance to look at my heater today but was told I would see the hex head once I remove the cover. The anode appears to be about 6-8 inches long according to what they showed me. What do you think?
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Old 03-12-2015, 07:43 AM   #6
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Surburban brand heaters have an anode, but I am not aware of any Atwood heaters having one. I don't see one on my Atwood heater. Of course my heater is 4yr old, so things could have changed.
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Old 03-12-2015, 10:58 AM   #7
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My Atwood is 7 years old and has no anode. No need for it because of the way it is constructed
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Old 03-12-2015, 11:14 AM   #8
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Originally Posted by acsnook View Post
FW28z,


I went to an RV store today to purchase the replacement plastic plugs. I was told that Atwood water heaters already have an anode, which should be replaced yearly, and was shown one. They also sell brass plugs (with a drain valve in the center) and stated their use is fine as the heater has an anode. I didn't get a chance to look at my heater today but was told I would see the hex head once I remove the cover. The anode appears to be about 6-8 inches long according to what they showed me. What do you think?
My 2015 Challenger has no anode rod and I verified that with the dealer during the PDI when he showed me where they stored the plastic plug after winterizing the unit. When I look at the configuration of the water heater I can not see any way to install an anode if I wanted to because of the location and angle of the drain plug hole. Also, the operators manual for my Attwood 6 gal water heater makes no mention of an anode rod.

One recommendation I will make is to always use a 6 point socket or box end wrench when removing or installing the plug. the use of a 12 point could round the end of the plug if that wrench or socket is worn or if it is not positioned correctly (angled on the plug end) for removal and/or reinstallation.

One additional point is that on my prior coach I had a Suburban hot water heater and it did have an anode rod. In that case, and I'm not sure about all cases, the anode rod and drain plug were one in the same. You had to remove the anode to drain the hot water heater. The general rule of thumb, and recommended in the that Suburban owners manual, was to replace the anode rod after draining the tank for winterization.
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Old 03-13-2015, 02:19 PM   #9
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I took a borescope today and looked at the inside of my Atwood heater:



At this point, I am not sure if it is corrosion or scale. When it gets warmer outside, I am going to attempt to flush it with a mixture of vinegar and water. If some of it comes off, I am assuming it is scale; but if there is no change, then I am going to assume it is corrosion.

I also measured between the brass overflow valve on the water heater to the aluminum threads that the nylon plug screws into, and I measured 0 ohms.

This means there is contact in water with dissimilar metals, so my conclusion then is that corrosion will occur inside the tank. Why Atwood does not see the need for an anode is puzzling... perhaps its part of planned obsolesce.

But, I have no data showing failure rates in Atwood heaters due to corrosion, so perhaps the corrosion rate is low enough that Atwood does not think an anode is required.

At any rate, corrosion has to be happening due to the dissimilar metal contact, whatever the corrosion rate is. So whether you use an anode or not probably just depends if you want dissolved magnesium or dissolved aluminum in your hot water.

Camco makes two different anode/plugs for Atwood heaters.

For me, it is a good indicator to keep taking a jug of distilled water along for coffee and meal preparation.
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Old 03-13-2015, 02:33 PM   #10
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Originally Posted by FW28z View Post
I took a borescope today and looked at the inside of my Atwood heater:



At this point, I am not sure if it is corrosion or scale. When it gets warmer outside, I am going to attempt to flush it with a mixture of vinegar and water. If some of it comes off, I am assuming it is scale; but if there is no change, then I am going to assume it is corrosion.

I also measured between the brass overflow valve on the water heater to the aluminum threads that the nylon plug screws into, and I measured 0 ohms.

This means there is contact in water with dissimilar metals, so my conclusion then is that corrosion will occur inside the tank. Why Atwood does not see the need for an anode is puzzling... perhaps its part of planned obsolesce.

But, I have no data showing failure rates in Atwood heaters due to corrosion, so perhaps the corrosion rate is low enough that Atwood does not think an anode is required.

At any rate, corrosion has to be happening due to the dissimilar metal contact, whatever the corrosion rate is. So whether you use an anode or not probably just depends if you want dissolved magnesium or dissolved aluminum in your hot water.

Camco makes two different anode/plugs for Atwood heaters.

For me, it is a good indicator to keep taking a jug of distilled water along for coffee and meal preparation.
Pic shows classic example of scale. Camco has a water heater rinsing wand, use that to clean the interior; that scale will flake right off. Atwood water heaters do not require an anode rod due to their construction. Don't use a metal plug; it will corrode and weld itself to the fitting. Camco sells a kit that has spare nylon plugs and a specialized two headed wrench.
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Old 03-14-2015, 03:30 PM   #11
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There is a video on you tube that describes the issue and how to flush the water tank. The procedure to flush may vary depending on whether or not you have a diverter valve.

The link to the video is

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Old 03-14-2015, 03:43 PM   #12
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I have one of those Camco water tank rinsers that I have been using.

But I am going to call Atwood and find out the real truth about why they do not recommend an anode. There is definitely the potential for corrosion due to the brass overflow valve being in contact with the aluminum tank.

I have to find out why they don't recommend one.
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Old 03-14-2015, 04:14 PM   #13
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Originally Posted by FW28z View Post
I have one of those Camco water tank rinsers that I have been using.

But I am going to call Atwood and find out the real truth about why they do not recommend an anode. There is definitely the potential for corrosion due to the brass overflow valve being in contact with the aluminum tank.

I have to find out why they don't recommend one.
FW,

Something I found

Another way of obtaining cathodic protection is to connect the aluminium object to the negative pole of an exterior DC voltage source.

The first way the article discusses is the use of an anode rod.

The way I understand the info above is that the direct grounding of the Attwood tank to the DC side of the coach would serve the same purpose as an anode rod in an aluminum water heater.

I haven't looked at my Attwood water heater's schematic but I wonder if the tank itself is grounded to the vehicle chassis or in some manner through the house batteries using some type of lug or jumper.
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Old 03-14-2015, 05:15 PM   #14
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It's just piquing my interest. And when that happens, I want to know more. I know that Atwood says an anode is not required, but I want to know why not, since I can verify there is dissimilar metals in contact with the water (brass valve and aluminum tank).

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Old 03-14-2015, 08:10 PM   #15
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Why not give Atwood a call? Couldn't hurt. (Of course they may just give you a bunch of sales mumbo jumbo instead of a real technical reason or the worst thing they could do is say "no".)
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Old 03-14-2015, 09:06 PM   #16
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That is my plan.
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Old 03-15-2015, 04:37 PM   #17
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New Thor Axis Hot Water Heater Problem

I'm not sure this is the best place to post this help request.
Just purchased a new 2015 Thor Axis 25.1. We're getting ready to use it on our first trip. After getting everything hookedup at home to test, I noticed the hot water was not getting hot. I then removed the drain plug on the hot water heater and nothing came out. Empty. I tried both external water and water pump hookups. No water in HW tank.
Is there a shut-off on the HW tank? This unit was not dewinterized by the dealer because it was still freezing here.(North Georgia)
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Old 03-15-2015, 04:42 PM   #18
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yes there are bypass valves. On the 24.1 they are accessed by removing the cold air return vent or by removing the base of the passenger side bed.
I'm not sure how you access them on the 25.1. Looking at the pictures of the 25.1 on the Thor website I would guess its the same for that model (remove cold air return vent).
This is what it looks like behind our cold air return vent:

If you look behind all the stuff (at the top of the hole you can see the white styrofoam insulation of our water heater) you'll find the 3 bypass valves.
(Note: The black box is the auto-switch for when the genny is running. I have since secured it to something a bit more permanent than just hanging by the 120V wires....Thor quality at its best!)

Hopefully you didn't run your water heater on 120V yet--you'll burn out the heating element with no water in it.
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Old 03-15-2015, 05:30 PM   #19
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Thank you JamieGeek, you were spot on.
I have 3 shut-off valves, 1 for the HW tank, 1 for the Water Pump and I'm not sure about the 3rd one.
Unfortunatly I did turn on the 120V HW heater. The tank is now heating up with LP and ELEC. Not sure if the Elec heater is working. But the water is getting hot.
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Old 03-15-2015, 08:51 PM   #20
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This is typically how Thor plumbs the winterization kit on the water heater:

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