Troubleshoot a Honeywell Thermostat That’s Not Working (2024)

At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if, in any doubt, it is best to seek the assistance of a professional.

Troubleshooting Procedure

I've broken this guide into two sections.

• Scenario 1: If your thermostat has a blank display and is not responding to any button presses, then continue reading.
• Scenario 2: If your thermostat has an active display that responds to touch, but, the heating or AC is not turning on or reaching the set temperature then jump to Scenario 2. In this case, the thermostat may possibly flash an error code or message like “cool on”, “heat on”, “wait”, or “waiting for equipment”.

Scenario 1: Troubleshooting a Blank Thermostat Display

If the display on your thermostat is not waking up to button presses or touch gestures for smart thermostats, it may be a malfunction or may be out of power.

Besides that, it can also indicate an issue within the internals of the thermostat.

So let’s walk through troubleshooting a blank display, step by step.

Step 1. Check if the Thermostat Panel is Pressed In

First, you want to check if the thermostat panel is firmly pressed in.

If it’s not, make sure to take it out, unscrew any fasteners, and re-install the panel. The thermostat panel should stay flush with the mounting plate.

Even if the panel isn’t loose, I highly recommend unplugging the thermostat panel and reinstalling it for good measure. While you’re doing so, make sure to follow the second step.

Step 2. Check the Thermostat Wiring

So while you’re unplugging the thermostat panel, it’s a good idea to check the wires for loose connections or damage.

The wiring configuration may vary based on your system, but always check for the red-colored R-wire and make sure it’s connected securely to the appropriate terminal.

Beyond that, you can check for the black-colored C wire, if your thermostat doesn’t run on batteries.

To learn more about thermostat wiring, you can check out this guide.

Step 3. Check the Batteries

After checking the wiring, it’s also a good idea to check the batteries, and possibly replace them if you haven’t done so in a while.

Even in cases of screen flickering, fading, or completely turning off, replacing the batteries might quickly solve your issue.

Most thermostats have batteries and still take power from the HVAC system, but some models work only on batteries. Nevertheless, replacing the batteries is always a good idea.

Also, don’t forget to check out my extensive guide on how to replace batteries for all Honeywell thermostat models.

Now, reinstall everything and see if the thermostat lights up.

Step 4. Check the Power

If the panel doesn’t power on, even after following through with the steps above, check the circuit breaker and the lights on your HVAC system.

Also, look for any safety switches near the unit. If your thermostat has one, make sure it’s flipped to the “on” position.

Step 5. Check Furnace Doors

If your thermostat is connected to a furnace, it is possible that the furnace door is not shut properly. Furnaces usually have a door switch and some thermostats are extremely sensitive to this as it’s a safety concern.

Check if doors are closed and sensors and indicators are working. If the door switch is broken or seems to have damaged wires, you might need to get it replaced with the help of a technician.

Step 6. Check the Voltage in the Thermostat Wires

If you’re comfortable tackling electrical components yourself, and you already have a multimeter on hand, you can check the DC voltage coming in from the HVAC system to the thermostat.

Remove the thermostat panel from the mounting plate and check the DC voltage between the R and C contacts. For most systems, they need to be around 24-30V.

If you find a lower voltage, it might mean a wiring error or fault within the HVAC system.

Optional Step: Try Bypassing the Thermostat

If you have a tool or a contraption to create a jumper wire, you can try bypassing the thermostat.

This isn’t a proper solution per se, but with this method, you can confirm if the issue lies within the thermostat and not the HVAC system.

To bypass the thermostat:

If the furnace or AC powers on without any issues, you can safely rule out the HVAC system. Then, the issue is definitely within the thermostat itself.

Conversely, if the HVAC system doesn’t work, you might have to troubleshoot it further.

Scenario 2: Troubleshooting the HVAC system not reaching the set temperature

In this scenario, your thermostat has an active display that responds to touch, however, the system is not reaching its set temperature. In this case, the thermostat may possibly flash an error code or message like “cool on”, “heat on”, “wait”, or “waiting for equipment”.

If a specific error code is showing, I recommend checking out this error code guide here.

Step 1. Change the Temperature

The first thing you can do if your thermostat display is on, but doesn’t power on the HVAC system, is to adjust the temperature.

So, first, try changing the temperature on your Honeywell thermostat.

Also, make sure the desired temperature falls within the acceptable ranges.

Specifically, set the heating between 40 °F to 90 °F (4.5 °C to 32.0 °C) and the cooling between 50 °F to 99 °F (10.0 °C to 37.0 °C). If you go beyond these ranges, the HVAC system won’t kick in.

Step 2. Wait 5-10 Minutes

If your display shows a “wait” message, or flashes “cool on” or “heat on,” you can simply wait it out for five minutes or so.

This step helps you safely rule out the compressor protection feature.

Step 3. Change the Temperature Mode

However, if the HVAC system doesn’t power on after that, try changing the temperature mode first. This can help the thermostat reconfigure itself.

Also, if you find that the heating unit works while the cooling does not (or vice-versa) you can easily tell that the issue lies within the component that doesn’t power on.

Step 4. Verify the Temperature Sensor is Working Correctly

In certain situations, although rare, the temperature sensor inside the thermostat, or the one connected to it, might be malfunctioning. In this case, it’s a good idea to verify the temperature using an external temperature gauge.

If the room temperature displayed on your thermostat or smart sensor isn't consistent with the reading on a thermometer, it might imply the sensor is faulty.

Faulty Smart Sensor

In the case of faulty smart sensors (like the T9 smart room sensor), you can unlink the sensor from the app and replace it with a new one later (or replace the battery in the sensor).

Fault in the Embedded Temperature Sensor in the Thermostat

If it’s the temp sensor in your thermostat that’s incorrect, you might have to get it looked at by a technician or replace it entirely.

Step 5. Check the Wiring

Weak splices, wrong or loose connections, and exposed wiring may cause issues and prevent your thermostat from working properly.

In this case, isolate the circuit, unscrew the thermostat, and check if the wires are connected correctly.

Check if Y and Y2 are attached to the correct color wire for cooling. For heating, check if W and W2 are attached to the correct color wire.

Also, you may want to verify if there are Rh and Rc wires in your system and whether they are attached to the proper terminals identified by the correct color.

Step 6. Check Individual Components

If possible, you can check all the individual components of your HVAC system.

This might include checking the switches, indicators, fuses, and wiring for your furnace, heat pump, and AC system.

Final Step: Call in the Experts

When all else fails and your Honeywell thermostat remains unresponsive, consider seeking professional help.

A technician can quickly identify and fix common issues, such as damaged wiring, malfunctioning capacitors, obstructed sensors, or blown fuses, while also inspecting components like the compressor, condenser, or fan motor.

Conclusion

Sources

• https://www.honeywellhome.com/us/en/support/air/thermostats/product-selector/device-not-working/
• https://www.honeywellhome.com/us/en/support/lyric-thermostat-troubleshooting-7/
• https://www.honeywellhome.com/us/en/support/why-is-my-thermostat-wifi-not-working
• https://www.honeywellhome.com/us/en/support/when-setting-up-my-t5-or-t5-plus-t6-pro-wifi-cannot-connect-to-my-wi-fi/