How Do You Troubleshoot a Honeywell Thermostat?

By Jack SteinLast Updated April 22, 2019
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Honeywell is one of the biggest names in home heating. Whether it’s a basic analog thermostat found in an older house or a state-of-the-art smart home interface that manages heating, cooling and more, countless Americans use Honeywell thermostats.

The company has a reputation for making solid and dependable equipment. As with any technology, however, things sometimes go wrong. While looking in the manual is often the best solution for troubleshooting a thermostat, you’re not alone by any means if you haven’t been able to keep track of it over the years. Fortunately, most problems with Honeywell thermostats are fairly straightforward to solve. With the solutions below, you should be able to identify and solve the most common issues with your device.

Checking Temperature Accuracy

Before you take apart your Honeywell thermostat, it's a good idea to confirm it's really misreading the temperature in the room. If your room thermometer and Honeywell thermostat match, then the problem is either with the AC or with your furnace. If the readings don’t match, then the thermostat sensor could be malfunctioning. If this is the case, you can choose between fixing the thermostat or purchasing a replacement unit.

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There’s one easy way to do that: a room thermometer. If you suspect that your thermostat is inaccurate, you should confirm that it's really misreading the temperature before doing anything else. To do this, take a room thermometer (not the kind you use to measure your own temperature) and let it take a reading. If your room thermometer and Honeywell thermostat match, then your problem is likely to be with your furnace or air conditioning rather than the thermostat itself. If the readings don’t match, however, then the thermostat’s sensor could be malfunctioning.

If that’s the case, you’ll need to either buy a new thermostat or recalibrate your old one. Unfortunately, the way to calibrate a thermometer can vary greatly between models, so you’ll need to identify what kind of thermostat you have before proceeding. Also, keep in mind that Honeywell thermostats are designed to account for radiant as well as ambient air temperature. A small difference probably isn’t anything to worry about.

Analog Problems and Solutions

Analog thermostats are much simpler than their digital counterparts, and troubleshooting one is simpler still. In most cases, problems are the result of the thermostat not being properly aligned. If the thermostat isn't level with the wall, the mercury switch could tilt and have problems reading the temperature in the room. If this happens, use a torpedo level to correct the alignment. The thermostat should also be at least 5 feet from the floor and in a location with no obstructions that could interfere with air flow.

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Dust can also cause Honeywell thermostat problems. To check and clean out the dust on the inside, remove the thermostat cover. With a soft brush or cloth, clear away the dust gently, taking care not to damage the electronics.

There could also be an issue with the wiring of the thermostat. If you feel confident (and ideally have your manual handy), you can try to see if any of the wiring is out of order — colors should match. Be aware, however, that you’ll need to turn off power to the thermostat first before attempting this, and you could damage the thermostat if you don’t know what you’re doing.

Blank Screens and Missing Readings

Is your digital thermostat not showing any information at all? If that’s the case and you (or someone else) recently took a look at your heating system, the problem could be the result of not closing the furnace door properly. The furnace door switch won't allow the HVAC system to turn on, which in turn prevents the thermostat from working. Shut the door properly, and your thermostat will likely return to normal.

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If the screen on the thermostat is completely blank, the circuit breakers for your HVAC or furnace could be tripped. Check your circuit breakers and then flip them on and off. If that doesn’t work, a fuse may need replacing. This can be a whole project of its own, so you may want to hire a professional to do it for you. However, it could also be a battery issue, which is potentially much easier to solve. Speaking of which...

What a Blinking Orange Light Means

If you see an orange flashing light on the thermostat, it probably doesn’t mean that your thermostat has stopped working yet, but it will if you don’t do anything about it. This light usually indicates a low battery, and it may even show the words “replace battery” or “lo batt.” While not all Honeywell thermostats use batteries, if yours does and that light comes on, you may have a limited amount of time before your thermostat shuts off (another cause of a blank screen, incidentally), although some thermostats only rely on battery power as a backup when they aren’t receiving it from the heating system itself.

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To change the battery, simply identify the battery case (there’s usually a seam) and open it. Many models take AA or AAA batteries, although some models may use others. Once you’ve replaced the old batteries, most of your settings should remain intact, although you may lose the date and time.If your battery draws power wholly from your heating system or the local power grid, there will be no batteries.

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