Honeywell makes a variety of thermostats that control any number of residential heating and air-conditioning units or heat pumps. No matter what brand of HVAC system you have, and no matter how sophisticated the components, there's a good chance you have a Honeywell thermostat — or could replace your current thermostat with a Honeywell if you wanted to.

A Honeywell programmable thermost with wi-fi controls.
credit: Honeywell
The most advanced programmable thermostats can even be controlled via a smart phone or tablet device.

Honeywell thermostats come in many forms, including older, analog thermostats. These are rectangular or (more likely) the familiar round dial-type thermostats that simply set a single temperature and then control the furnace and air conditioner to hold the temperature near that chosen setting. There's nothing very "electronic" or high-tech about these devices — they are purely mechanical in how they operate. These thermostats usually work with a simple vial of mercury inside them and a heat sensitive bi-metal coil that expands or contracts as temperatures in the room shift. However, despite their lack of high-tech sophistication, these thermostats are remarkably dependable, and many have been working for decades since they were introduced in 1953.

Modern Honeywell thermostats, though, are highly sophisticated digital electronic devices that can automate the HVAC system to program heating and cooling cycles for up to four different settings for each of the seven days of the week. You can, in other words, set these more advanced thermostats to automatically adjust temperatures to as many as 28 different settings over the course of a week. Simpler models offer two levels of programming — one for the Monday-Friday work week, and another for the Saturday/Sunday weekend. So popular are these digital Honeywell thermostats that many other brands' thermostats are actually manufactured by Honeywell and are programmed in exactly the same way as the comparable Honeywell models.

Both analog and electronic Honeywell thermostats are remarkably dependable, but occasionally problems do arise.

Trouble-Shooting Analog Thermostats

A Honeywell dial thermostat.
credit: Midnightcomm—Flickr Creative Commons
Older dial-type Honeywell thermostats are remarkably dependable.

Analog </ahref="http:>thermostats may be round or square, depending on the model. These thermostats usually have a HEAT, COOL or OFF setting and an AUTO or OFF _s_witch position for the fan.

  1. To test for heat, turn the thermostat to the HEAT position; set the temperature as high as it will go, such as 80 degrees F, and wait five minutes for the furnace to activate. If you hear or feel the furnace kick in, it is operating correctly.
  2. Set the switch at the top of the thermostat to COOL and the fan switch to AUTO. Turn the dial or set the temperature switch to the lowest setting, such as 60 degrees F. Wait five minutes to see if cool air begins to flow. If you hear or feel the AC unit kick in, it is operating correctly.
  3. If neither of these actions turns the heater or air conditioner on, remove the cover to verify the small colored wires are connected properly inside the unit, as per the color-coded wiring diagram in the user manual. In the majority of cases, it is a simple matter of restoring the low-voltage wire connections to return the thermostat to proper operation.
  4. If the wiring is fine, there could be a problem with the furnace or air conditioner — or you may have to replace the thermostat because of its age. Now would be a fine time to install a newer electronic programmable thermostat.

Trouble-Shooting Digital Programmable Thermostats

Digital programmable thermostats come in a variety of model numbers and types. Some have keypads with digital displays; some have touch screens, while newer, more expensive models can even let you control the thermostat from your smart phone, tablet or computer.

Here are some of the most common problems with digital programmable thermostats, and the most likely solutions.

No Display

The most common problem with digital thermostats is a display screen that has nothing on it. Common reasons for this include:

  • The access door on the furnace is open or not fully shut. Some modern furnaces have a door switch that engages when the door is closed properly, thereby activating the entire system. When the door is not shut correctly, the door switch is not depressed and cuts power to the thermostat.
  • The batteries in the thermostat may be dead. If your thermostat has batteries, replace them, as this could cause the same problem. Most thermostats equipped with batteries may have a battery alert that indicates when to replace the batteries via a message on the screen
  • The circuit breaker for the furnace or air conditioner may have tripped. Most building codes require the furnace and the air conditioner to have their own dedicated circuits, so if either the furnace or the air conditioner aren't working, it is possible the circuit breaker has tripped. Flip the breaker switch to the OFF position and then back to the ON position.

Thermostat Fails to Operate Correctly

If the thermostat display is active but the thermostat is failing to control the temperatures as you want, check out these possible causes:

  • Low-voltage wires are disconnected. Inside the thermostat, the small colored wires that run from the thermostat to the various components of the system must be installed in their correct positions. If they are not, the thermostat won't operate. Some systems only require three wire hookups, while others can require up to six or more, depending on how many components your system includes. Refer to the color coded chart for your particular system when you need to reinstall a loose wire.
  • Time-of-day and day-of-week clock may be set incorrectly. The internal clock function can lose its setting, especially after power outages. While the internal battery is supposed to hold the clock settings if the system loses power, this does not always operate correctly. Verify the clock is set to the right day and time. With electronic programmable thermostats, the wrong day and time can prevent the system from operating correctly. Follow the steps from the owner's manual to set the correct time based on your model number found on the back of the thermostat.
  • Jumper settings may be incorrect. Remove the cover to verify that the jumper settings (found on some thermostat models) are correct. Some Honeywell thermostat models require that you set the jumper in the correct position for the type of furnace, air conditioner or heat pump you have. For example, some Honeywell thermostats require the jumper in the HE setting for an electric furnace and the HG setting for a gas or oil furnace. This ensures the fan activates when switched to automatic mode.

Problem With Furnace or Air Conditioner

It's also possible that the problem isn't with the thermostat at all but instead lies with the furnace or air conditioner unit, or with another component, such as a humidifier or air-exchange unit, if your home is so equipped. To evaluate this:

  1. Verify the thermostat is in COOL mode by pressing the SYSTEM button, and lower the temperature to its lowest setting with the fan set to AUTO. Wait five minutes, and listen for the unit to come on.
  2. Repeat these steps for heat, with the fan set to AUTO. Press the system button until HEAT appears on the screen, and set the thermostat at its highest temperature setting. Wait five minutes to ensure the heating unit comes on.
  3. When either of these actions fails to turn on the furnace, heat pump or air conditioner, the problem is probably not in the thermostat but is more likely to be found in another component of the HVAC system. This is especially likely if the thermostat is new and you have already verified that the wiring is correct.