Hot Wire of Broken Thermostat in Case of Weather Emergency

Something that is often neglected, even by active people who really check the heat before the first frost, is the humble thermostat. That tiny appliance on your wall—whether it’s an old-fashioned mechanical thermostat, a humble battery-operated programmable version, or one of those smart thermostats that steals all your personal data —is crucial in cold weather. If your thermostat stops working, your heating won’t turn on.

It doesn’t really matter if it’s in fine weather—a quick trip to the hardware store or calling a handyman or HVAC contractor will quickly install a new thermostat . But if your thermostat breaks during a raging blizzard or in the middle of the night in sub-zero temperatures, you’ll experience discomfort at best and dangerous at worst.

Fortunately, the thermostat is a fairly simple device and you can get around it without much tools or special knowledge. Here’s how you can turn the heat on in an emergency, even if your thermostat has given up.

Thermostat Wiring 101

First, a brief overview of how your thermostat is connected. Note that there may be some variation in this – certain HVAC systems will sometimes have a slightly different wiring configuration, and depending on your exact setup, you may not have all of the wires listed here, or you may have some additional ones. But these are the basics you need to know for the ugly hack you can pull off.

First, remove the thermostat from the wall. This may require screws, or you can simply snap it off the clip attached to the wall. There you will see a small circuit board with wires coming out of the wall, screwed to the terminals. Each of these wires is color-coded, and each terminal most likely has a letter code:

  • Red : The red wire is the wire that supplies power to the thermostat and connects to the terminal marked “R”. If you have both heating and cooling, you may see two separate terminals labeled Rc (or cooling) and Rh (for heating).
  • Green: The green wire connects to the “G” terminal and starts your system’s fan. However, not all systems have a fan, so you may not see it.
  • Black or Blue : These wires connect to the “C” terminal and are the neutral or common wire.
  • Yellow: The yellow wire connects to your cooling system and uses the “Y” terminal.
  • White: The white wire controls your heating and connects to the “W” terminal.

Again, your home’s HVAC system can be more or less complex than this . For example, if your thermostat only controls the oven and not the air conditioner, you might only have a red and white wire. And if the person who wired your thermostat was lazy or inexperienced, they may have ignored color coding conventions, so make sure the color matches the terminal. In other words, if the green wire is connected to the R terminal, it is most likely the power wire, but be especially careful because the job was not done correctly.

Assuming your thermostat has been properly wired, the good news is that you only need to worry about three wires for heating on a cold evening: red, white, and green.

Thermostat connection

If the heating has stopped working in the house, but the electricity is still on, the first thing you need to do is to check if the problem is with the thermostat, stove, or boiler. Check if your thermostat is using batteries and replace them if so. Most battery operated thermostats will alert you when the battery is low, but this is an important first step if you don’t want to feel stupid.

If the battery is fine, your next step is to check if the thermostat is receiving power, if possible. To do this, you’ll need a voltage tester , which is generally handy if you’re the kind of person who considers opening things like thermostats and touching wires coming out of your walls. Touch the tester wires to the R and C terminals of your thermostat. You should get a reading of 24 to 30 volts. If you’re getting less than 20 (or nothing at all), you’re in big trouble and bypassing your thermostat won’t help. You will most likely need to contact a HVAC specialist or an electrician.

If you get good voltage, your thermostat may be broken, so bypassing it may work. Assuming you removed the thermostat from the wall and exposed the wires, unplug the oven to avoid a nasty electric shock. If you don’t know how to turn it off on the oven, you can turn it off at the switch. However you do it, make sure you’re not dealing with live wires.

Once this is done, there are three approaches you can take:

  1. Literal hot wire. If you’ve seen the old movie depicting someone crossing the wires in a stolen car to start the car, it’s the same concept here: unscrew and remove the red (power), white (heat) and green (fan – if present). wires from the respective terminals and twist them together. When you turn the power back on, your heating should be in full force. If there is no green wire, just twist the red and white together. Pro Tip: If the wires seem to be slipping through the wall, stick a pencil or other object behind them to prevent this.
  2. Jumpers. Use alligator clips or magnetic jumpers to connect the red, white, and (if available) green terminals. Again, as soon as the power is in place, the heat should start immediately.
  3. MacGyver is. Don’t have specialized power tools and don’t want to twist wires? You can connect the red and white wires with another piece of wire – just strip both ends and connect the bare ends to the R and W terminals, screwing them into place. In a pinch, you can even use a paperclip – all you have to do is create a connection between power and heat.

Note that you can also turn on the air conditioner in the same way if there is a heat emergency and your thermostat fails: instead of the white wire, connect the red and green wire to the yellow wire connected to the Y terminal. Also note that neither under what circumstances should you not connect the red and black or blue wires connected to terminal C. This will burn the circuit board of your oven and you will have a mess on your hands.

Finally, keep in mind that this is for emergencies only. This will cause your heating (or air conditioning) to run all the time, which these systems are not designed for. This will damage your HVAC systems over time, so be sure to replace the thermostat as soon as possible and/or turn off the power to give your oven a break.


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