Replacing 120V Wires on WH Thermostat

[Carl n Susan]

Well after a couple of failures of the hot water heater 120V thermostat the latest one cooked the wires. So in addition to another thermostat I also need to replace the wires. The thermostat is easy.

The black wires comes from the rocker switch up to the low side of the thermostat and the upper black wire goes to the heater element (as I understand it). As you can see the damage goes down the wires to where you can't get to it. And there is no more slack. The question is how do you get access to these wires in order to replace (or splice into them)?

Do you remove the outside trim panel? Does the WH have to be pulled out? Having never done this before I am hoping to tap into the experiences of someone who has.

[rohrmann]

I think you will need to pull the water heater out, at least far enough to access the box where the relay is located. You will probably need to disconnect the propane line, but if you don’t have to completely remove it, you might be able to leave the water lines connected. When I replaced our water heater in 2016, I was able to do the swap in a couple hours, and that included transferring the relay box from the old unit to the new one. There are some screws that need to be removed and the caulking at the flange where it attaches to the outside wall needs to be cut to allow the unit to be pulled out. You will also need to cut the caulking around the propane line.

[psomers]

Can't you get to the wiring behind the WH from the pass through storage? Panel removed of course. Never done wiring but did replace WH check valve with out WH removal.

[Carl n Susan]

I should be able to get behind the WH through the pass through compartment. But I am hoping that as the two wires only run on the front of the WH, (switch to thermostat and T_Stat to heater element) I shouldn't need to get to the back of the WH. Hopefully I can fish new ones using the old ones. I was hoping someone had done this before to verify this approach.

[rames14]

Best of luck Carl. I don’t even have a unit here to look at to get a view. Our old unit is at the dealer already waiting for us to PDI our new one. I’m sure you will get it fixed in short order. Are you able to run off propane for now?

[Carl n Susan]

Yup running off of propane but I prefer to use the park's 50 amp service.

[AZ Traveler]

I am shocked that there is something that Carl has not previously fixed on a Montana.

[mlh]

Originally Posted by AZ Traveler

I am shocked that there is something that Carl has not previously fixed on a Montana.

Shocked and amazed. Carl is the guy we go to for answers.
Lynwood

[Carl n Susan]

You guys give me too much credit. There are a lot of things the members here have experienced that I have been lucky enough to avoid. One of them used to be burnt wires in the WH. Not any more. I really wanted to be done with learning new repair methods. But I do own a RV

[Montana Man]

Originally Posted by mlh

Shocked and amazed. Carl is the guy we go to for answers.
Lynwood

That's what I was thinking!

[432bartman]

Carl, good luck with this repair. In the future, the rest of us on this forum will benefit from it.

[jeffba]

And Bob doesn't look like he has done this either.

This is amazing!!

[rohrmann]

I’ve never had a wiring failure in the water heater. Early on, had trouble with the unit, replaced a couple items until I discovered the 120 volt thermostat was bad, replaced it and all was good. Later on I found that Suburban had gotten a bad batch of thermostats, had a red reset button on them and that was what I had that failed.
About five years ago our tank developed a leak, so I replaced the water heater, and just transferred the junction box with the relay in it to the new unit. This was pretty easy, and on our rig, the water heater is right next to the convenience center, so accessing the water connections wasn’t too hard. The junction box sets right up against the wall of the convenience center, and as I said, when replacing the Hepvo valve last week, at least on our rig, the junction box is visible but not in a position where one can get two hands on it or even get a screwdriver or other tools at it.
I would also suggest using heat resistant wire when replacing the wiring. I’m also thinking that there might be a problem with the element that might have caused the wire failure. It will be interesting to hear what all was needed to complete the repair.

[Carl n Susan]

Thanks Bob. I too went through the defective batch of thermostats and have had lots of experience changing them.
The Suburban documentation recommends 14 gauge heat resistant wire and I have that on my shopping list.

As for the element, I plan to check it out too. I don't see how its failing, it had been running for three days when things went south, could fry the wire. It should just go open and then there is no circuit. But I will take a hard look at it.

I suspect the cause is related to the sheet metal rubbing on the wires causing them to fray and ground out. There is a sharp edge on the cover where the wires run under to the switch and heater element.

I will be home this weekend and I can easily work on it there. In the meantime I am using propane for heat. No big deal.

[rohrmann]

If you were down here in Arizona where we are now, you wouldn’t even need gas either to heat the water. It cooled down today to the low 90’s, and water from the tap doesn’t really get cold.

[BB_TX]

Just my musings, but looking at the picture it appears the lower lug overheated to the point the insulation may have actually caught fire momentarily . And that fire burned the wire and lug insulation above it. And that type overheating directly on that lower lug is typical of a bad electrical connection generating heat due to line resistance. Doesn't take much in the way of resistance to create a lot of heat.
A grounded wire is more likely to trip the breaker before it would burn the wire like that. At least in theory.

[beeje]

The junction box on the water heater that contains the 12 volt relay on our unit burnt up last year. I eliminated that and installed a hundred and twenty volt switch in the bathroom to control the heater. Now the 12 volt switch in the panel does nothing
Shouldn't be too difficult to replace a wire. Try to tape the new wire onto the old one and use it as a pull string from point A to point B. I am not an electrician and my only question would be what wire to use. Stranded THHN ?

[Carl n Susan]

Taping a new wire to the old to use as a pull string is the plan. I am just worried about how tight the sheet metal is to the heater and if the wire will pull through. I will find out today. Suburban says to use 14 gauge wire rated for 105 degrees Centigrade (that is 221 degrees Fahrenheit for us non-metric folks). Amazon had 14 ga. rated to 300 degrees Fahrenheit.

[beeje]

I think I would use 12 gauge just for a little insurance

[Carl n Susan]

Well the repair is complete and wasn’t as bad as I envisioned it could be. The two fried wires went from the On/Off switch to the thermostat and from the thermostat to the heater element. The wire from the relay to the On/Off switch was fine. That is wonderful as access to the relay requires removing the water heater (or at least pulling it halfway out or so). On a full body paint RV, paint lines never seem to line up when you put it back together.

My other concern was what was behind the sheet metal that covers the front of the tank. Would I be able to pull new wires without disassembly? And the answer is Yes, the wires run free behind the sheet metal and while snug, you can pull them out.

Taping a new wire to the existing wire was the plan for running the replacement wires. That did work wonderfully for the wire from the thermostat to the heater element. The wire from the On/Off switch was pretty short at the thermostat end (because it was really fried) and I forgot to tape the new wire to it before I futzed with the switch itself. Of course, when the switch came out of the sheet metal the far end of the wire at the thermostat disappeared. Bummer! I was able fish a stiff wire down to the switch hole and then used it to pull the new wire. But I wasted a lot of time fishing that wire. Moral of the story: tape the new wire on before doing anything else. The Suburban manual states you are to use high temperature 14 gauge wire rated at 105 degrees Celsius (221 degrees Fahrenheit).

Both the thermostat and the On/Off switch have male spade terminals. Because of the tight space, 90 degree “Flag” female connectors are used. The rocker switch has 1/4” spades. You can buy the 1/4” female connectors most anywhere. The thermostat however has 3/16” (0.187”) spades and require a different connector. These are hard to find in automotive/stereo shops. One place to get them is listed in the Parts List below.

While I was working on the repair, I got a call from a MOC friend who had the same problem on his almost new SOB. He believes his smoke cause was a wire frayed by rubbing on the sharp edge of the sheet metal. The result was still a smoked thermostat. I decided to do a little overkill in my repair. First I added heat shrink tubing to the wires to add extra protection against fraying. Second I used 1/4” drip line tubing that I slit and put over the exposed edge of the sheet metal. Between the two mods, there should not be any future fraying of the wires.

Parts List
Suburban Manufacturing Suburban 120V T-Stat/Limi 232306 *Clicky*
Electrical Wire 14 AWG 14 Gauge Silicone Wire High Temperature Resistance *Clicky*
90° Flag Quick-Disconnect Terminals – 1/4” and 3/16” *Clicky*
Heat Shrink Tubing 1/4”
Drip Line Tubing 1/4”

This picture is with everything opened up and the new wires run.


Here is what it looks like after everything is repaired. The drip tube insulation on the upper edge of the sheet metal is barely visible. Note I had finally removed the propane line and the propane burner. They block the cover of the heater element. While I got it off with all that stuff installed, putting it back was not worth it.