I was about to replace an old single pole thermostat with a new double pole one when I discovered quite the shocker. When I took the old thermostat out of the wall, I immediately noticed there was no box. Someone had just chiseled out enough room for it in a stud!

Oh yes, it gets better. The blacks from each set were together and connected to the line terminal. The whites were together and connected to the load terminal. Normally I would think that this would be bypassing the thermostat altogether, but somehow it was still acting as a switch. :confused:

And oh yes, it gets even stranger. I separated the wires out and flipped the breaker back on. I then proceeded to test each set of wires and find that both sets are reading 240v! :eek: Okay, now I'm getting really confused. This setup has worked 30+ years somehow. I walked over to the heater and ran my non-contact tester by the floor where the wires go in and it was picking up current there as well. I don't know how much yet.

Now, I highly suspect that the two closets in that room were added later because the wires come out at the end of the second one. There are also two sections of drywall (one on the back, one on the side,) inside the closet that you can tell someone cut and replaced. My best guess is that the thermostat used to be located on that back wall and then someone figured out a closet wasn't a good place for a thermostat and decided to move it. They obviously had no idea what they were doing and now because of it, I don't either...

How this setup has worked for all these years and not burned the house down, I have no clue, but one things for sure, it needs to be fixed. I think a good place to start would be to cut those pieces of drywall out and take a good look at the wiring in there. They had to have used some wire for extension. I can't for the life of me figure out how there are 4 hot wires and yet the heater does not run 24/7. :confused: Does anyone have a clue what's going on here?

Short answer to this,

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Originally Posted by techcw

Does anyone have a clue what's going on here?

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Is No, besides being very lucky that even something is definitely wired wrong, with power coming at the stat from two directions, and somehow it worked.

I hate when I try to do a simple 10 minute job and end up finding a rat's nest such as this.

Do not use a non-contact tester when trying to troubleshoot. Use a voltage tester with leads.

All the cables need to traced and determine how they are connected, and correct any miswire conditions, along with correcting issues like line voltage splices not contained inside boxes.

You have to remember that the heater is almost essentially a wire,so measuring voltage across a switch when it's off would be 240 V. It's capable of applying appreciable power because the resistance is low.

While true, power is normally run to the thermostat first in these instances so that both leads may be broken in the off position. Again, note that DPDT thermostats act odd. One side of the line breaks on temperature rise. The other breaks only when the stat is off.

"switch loops" normally mix up the wihite and black wires and that's why your supposed to re-code the end of the white wire as black. The white coded black is supposed to be power (LINE). The black is switch LOAD.

Well, I cut out those two sections of drywall out and traced the wiring back to the original thermostat box. The white wires were wire nutted together like the rest of the ones with the old single pole thermostats had been. No problem there, but what I found was that someone had two sets of wire coming from the black ones. I won't even bother explaining how this mess was wired. It made no logical sense. I disconnected those wires and tested the ones in the box. All was how it should be.

I easily found a suitable location for a box to be mounted. Why they chose to chisel out a stud, I have no idea.