A Honeywell smart thermostat is a great way to fine-tune how you use your heating and cooling. But like any technology, you may sometimes experience a problem. With the digital display, Honeywell smart thermostats can display an error code that trained technicians can use to understand what's going on. Here are a few of the most common error codes you may see on your Honeywell smart thermostat.

Error Code e42 for Honeywell Thermostats

You may receive this error code when your home’s Wi-Fi connection did not provide an IP address for the thermostat to hook up to. This can occur if the router fails to perform the Dynamic Host Configuration Protocol, or DHCP. This process automatically supplies the necessary IP address for your thermostat to link up.

How to Fix Honeywell Thermostat Error e42

You can resolve error code e42 by making sure that your router can complete the DHCP. If it does, you usually also need to power cycle the router and repeat the initial setup process with the thermostat. Doing so should ensure the DHCP is sent and connects to your smart thermostat.

Honeywell Thermostat Error e02

Error code e02 appears if the password for accessing your home’s Wi-Fi router is incorrect. After this error code is displayed for 30 seconds, the thermostat’s digital display will automatically progress to the Wi-Fi setup screen so you can try the password again.

How to Fix Honeywell Thermostat Error e02

All you'll need to do to solve error e02 is ensure you’re typing the correct Wi-Fi password when setting up the thermostat.

Honeywell Error Code 40

Error code 40 can show up when the thermostat is notified that a heat pump or air conditioner’s monitoring system has detected a malfunction. Most commonly, this occurs when the compressor isn’t running despite being directed to. But this error code can also appear if power is shut off from the outdoor unit for an extended period of time. A “High Pressure Fault” error, caused by poor airflow, can render this error code. And finally, you may encounter error code 40 if there’s something wrong with the coolant, the outdoor unit’s fan motor or the motor’s starting capacitor.

How to Fix Honeywell Thermostat Error 40

You can check the air filter for signs of a clog, as well as the breakers and indoor unit’s blower for ordinary operation. If you reset the thermostat and error code 40 reappears, it’s best to contact an experienced technician.

Error Code e43 for Honeywell Thermostats

If your Honeywell thermostat shows error code e43, it is unable to communicate with the router, and by extension your Wi-Fi. This can happen if the router’s ethernet cable isn’t plugged in or it isn’t communicating with the wide area network (WAN).

How to Fix Honeywell Thermostat Error e43

Reboot the router by unplugging it and leaving it that way for about 30 seconds. The thermostat might also be disconnected if you recently switched the password or the Wi-Fi’s SSID, which is the name you give it.

Error Code e1 for Honeywell Thermostats

Thermostats employ sensors to identify the temperature outdoors and indoors. If a sensor fails, you may see error code e1 appear on your Honeywell smart thermostat.

How to Fix Honeywell Thermostat Error e1

A trained technician can replace the sensor and restart the thermostat, which should clear error code e1.

Honeywell Error Code 11n

Error code 11n could appear when the thermostat can’t recognize a heating or cooling unit. This can mean that the equipment itself is defective and unable to communicate with the thermostat. This sometimes happens when the wiring is bad or even if the thermostat is faulty.

How to Fix Honeywell Thermostat Error 11n

A professional technician can utilize a voltmeter to assess if there’s a faulty electrical connection. In situations where the wiring on your specific HVAC system is bad, the technician can replace it. In situations where the thermostat itself is the issue, it will likely have to be replaced.

Honeywell Thermostat Error e2

If you’ve noticed error code e2 show up on your Honeywell smart thermostat, it could mean several different things. Sometimes, one of the sensors used to detect the temperature isn’t operating correctly. In other instances, it means the router was disconnected from its power source before the thermostat finished the setup process.

How to Fix Honeywell Thermostat Error e2

When the error code stems from sensor failure, a technician can troubleshoot and switch out the affected sensor. If the problem originates from disconnected power, all you'll need to do is verify the router stays on throughout the setup process.