Last year I installed a bunch of Aube TH115 programable thermostats. Five of them to be exact. They are line voltage thermastats that control our 240 volt baseboard heaters. I also had bought a couple Aube TH114 non-programmable thermostats as well. These were to go into a couple downstairs rooms that aren’t used very much. Currently installed in those rooms are a couple very old, very ugly Intertherm thermostats.

Intertherm

Tonight I decided to install the Aube TH114’s. First, I shut off the breaker that I had labelled basement heat. I pulled the cover off the thermostats in the crafts room. I unscrewed it from the wall, then tested it with my voltage tester. No power there. So I removed the wire nuts from the wires, and kept track of which wire was attached where, But there were no marking on the old thermostat that I could see saying which were the line wire, and which were the load. I made sure the wires weren’t touching anything. I turned on the breaker, tested the wires, found the ones with power, then shut off the breaker again. Then hooking up the new Aube thermostat was a snap. I turned on the power, and the thermostat came to life!
I turned off the breaker again. I misplaced my voltage tester. I checked the thermostat I had just installed, and it had no power. Great! So I pulled the cover off the old thermostat, and unscrewed it from the wall. I went to unscrew the wires, when sparks started shooting! Ouch! This thing was still live! Apparently it was on a different circuit. It melted the tip of the screwdriver.
Screwdriver

I hunted around the house, and found the voltage tester. Apparently I had thrown it away with the first old thermostat. I checked the breakers, but none had tripped. I started shutting off breakers, and testing the thermostat with the tester. Once I found the right breaker, installing the second thermostat was a snap!
Aube-TH115