Thermostats that control home heating and cooking systems seldom break, but when they do, most are easy to diagnose and fix. Even replacing a broken or outmoded thermostat usually is not too difficult.
If a furnace or central air conditioner fails to start, try turning the thermostat’s setting up (on a heating system) or down (on a cooling system) about 10 degrees. Doing so should start the unit. If not, go to the main service panel or fuse box and check for a tripped circuit breaker or blown fuse.
Reset the breaker or replace the fuse if necessary and try again. If the system still does not start, check that the furnace or air conditioner itself has not shut down because of a malfunction. After eliminating these possibilities, suspect a faulty thermostat.
Virtually all room thermostats operate on low voltage that carries little risk of harmful electric shock. However, it is always wise to shut off power to a thermostat at the service panel before examining or working on it.
Don’t tamper with a thermostat that controls an electric baseboard heater; these usually carry full-strength household current and can deliver a fatal shock. Have the unit inspected by a heating technician or an electrician instead.
*
To work on a thermostat, remove the cover and blow away any dust clinging to the inner parts. Look for small metal buttons called contacts that spring together when the thermostat works, completing a circuit that starts the system.
Not all thermostats have contacts. On those that do, adjust the thermostat setting to close them, then slide a coarse paper between the contacts to clean them. Do not use sandpaper or other abrasive material.
Also check for broken parts -- especially the coiled bimetallic spring that is the heart of most thermostats. If you find broken parts, replace the thermostat. Refasten loose wires by wrapping them clockwise around their terminal screws and tightening the screws firmly. Sometimes the screws are on the back of a thermostat plate. Remove the plate to reach the screws.
Burned wires can signal an electrical or fire hazard. Have any such condition inspected by a heating technician or an electrician immediately.
Restore the power and try to start the system again with the thermostat. If nothing happens, bare the ends of a spare piece of any insulated copper electrical wire; then, while holding the wire by the insulated portion, touch the wire ends to the terminals on the thermostat marked “R” and “W.” If the heating or cooking system starts, the thermostat is defective; replace it.
None of the above tests can be made on newer electronic thermostats, which have printed circuit boards. If these fail, consult the owner’s manual and try installing new batteries. Replace the thermostat if the problem remains.
To replace a thermostat, first shut off the power at the service panel. Remove the cover and plate, and then label the wires with pieces of masking tape identifying their terminals.
Unfasten the wires. Unscrew the thermostat from the wall and lift it away, being careful not to let any wires slip into the wall where they will be lost.
Thread the wires through the rear of the new thermostat and attach the thermostat to the wall, using a level to make sure it is horizontal.
Connect the wires by following the labels and the directions supplied with the thermostat. Attach the front plate and any batteries; then attach the cover, restore power and test the thermostat by using it to turn on the system. Finish by programming the thermostat or setting it as required.
FAQs
To be certain you have cut power to your thermostat, switch both circuit breakers to off. Then, confirm that the power is off by increasing or decreasing the temperature on your thermostat and waiting five minutes.
Do I need to turn off power before replacing thermostat? ›
Turn Off Power to the HVAC System
The first step in how to install a thermostat is making sure the power is turned off to your existing thermostat. Turn off the power for your heating and air conditioning system at the main service panel. Its circuit breaker should be clearly labeled.
Is it possible to turn off a thermostat? ›
Finding and unplugging the power supply is usually the first step in turning off a thermostat. The following are general actions you can take: Find the Panel of Circuit Breakers: Typically, a circuit breaker is used to link the thermostat to the electrical system in your house.
Can you install thermostat without turning off breaker? ›
You don't need to shut it off at the breakers in your electrical panel, but you should flip the power switch off at the unit or units the thermostat is operating (furnace, air handler, boiler, etc).
How do I turn off the power to my Honeywell thermostat? ›
Turn off power supply
For your safety, turn off power at the breaker box or switch that powers your furnace or air conditioning. Note: Turning off your thermostat won't turn off the power to the furnace or heating equipment.
Why is my thermostat not turning off? ›
It could be the wrong thermostat setting is being used, a clogged air filter or your thermostat itself is no longer working properly. When you have a heating system not shutting off, this issue makes it difficult to maintain the desired temperature inside the home.
Is it safe to touch thermostat wires? ›
Your best bet is to always turn the power off before touching any wires in the system. You can receive a shock from any level of voltage.
Do I need to turn off thermostat to change battery? ›
First, turn off the thermostat. Gently slide the thermostat housing up and off the wall mount plate. If it doesn't slide up/off or up/back-tilt, you can probably just pull it off. Look at the back of the thermostat to see what kind of battery is required.
Where is the breaker for my thermostat? ›
In this case, there are two ways that you could notice a breaker switch for your HVAC system. The breaker switches will either be located in a breaker box in your garage or outside near the unit in a smaller metal box. Most of the time, there are multiple breaker switches.
Is it OK to turn off thermostat in summer? ›
When you turn off the air conditioner in the heat of summer, you allow humidity to creep inside, and with it, mold and bugs creep in, too. That's why it is always best to turn the thermostat up instead of turning it completely off because air conditioners act like dehumidifiers, cooling and circulating the air.
While some homeowners have considered turning off their heat at night in an attempt to lower their heating bills, it generally is not recommended as a viable option.
Why is air still blowing when thermostat is off? ›
If your AC system short circuits, it won't be able to communicate with your thermostat. Therefore, any signals that you are trying to send from thermostat won't be passed along to your air conditioning unit and it will continue to run.
Does thermostat have its own breaker? ›
The thermostat, on a separate circuit, connects to the breaker with another wire connected directly from the heating unit. If the thermostat is low voltage, relays or transformers may be required.
What happens if you block a thermostat? ›
Unfortunately covering your thermostat prevents it from accurately reading the temperature in your living space. That's because it could cause the thermostat to “think” the area it's in is warmer or cooler than it actually is.
How do I find the breaker for my thermostat? ›
In this case, there are two ways that you could notice a breaker switch for your HVAC system. The breaker switches will either be located in a breaker box in your garage or outside near the unit in a smaller metal box. Most of the time, there are multiple breaker switches.
Why is my thermostat still running? ›
One of the most common issues is the thermostat. The wiring, switches, or heating sensors can fail on your unit. If this is the case, then you'll need to replace the thermostat with a newer model. A damaged primary controller can also cause the furnace to stay turned on.
Why does thermostat keep running? ›
A faulty thermostat can cause your furnace fan to run constantly. Your thermostat should be checked for proper calibration, battery condition, and settings to ensure that it is working correctly. If you suspect an issue with the thermostat, try replacing the batteries or checking the wiring connections.
Are thermostats on their own breaker? ›
The thermostat, on a separate circuit, connects to the breaker with another wire connected directly from the heating unit. If the thermostat is low voltage, relays or transformers may be required. Wire relays and transformers between thermostats and heaters or thermostats and breakers.
