A Honeywell smart thermostat is an excellent way to optimize how you use your home comfort system. But like any technology, you may occasionally experience a problem. With its digital display, Honeywell smart thermostats can display an error code that trained technicians use to get a better sense of what's wrong. Here are several 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 if your home’s Wi-Fi connection did not provide an IP address for the thermostat to hook up to. This can occur if a router does not complete the Dynamic Host Configuration Protocol, or DHCP. This function automatically transmits the needed IP address for your thermostat to link up.

How to Fix Honeywell Thermostat Error e42

You can fix error code e42 by verifying 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 your thermostat. Doing so should ensure the DHCP is transmitted and connects to the smart thermostat.

Error Code e02 for Honeywell Thermostats

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

How to Fix Honeywell Thermostat Error e02

All you have to do to resolve error e02 is ensure you’re putting in the correct Wi-Fi password when setting up the thermostat.

Error Code 40 for Honeywell Thermostats

Error code 40 can appear when the thermostat is informed that a heat pump or air conditioner’s monitoring system has detected a malfunction. Most often, this occurs when the compressor isn’t running despite being instructed to. But this error code could also appear if power is disconnected from the outdoor unit for a long period of time. A “High Pressure Fault” error, induced by poor airflow, can lead to this error code. Finally, you might experience error code 40 if there’s a problem with the refrigerant, 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 regular operation. If you reset the thermostat and error code 40 reappears, you should try to get a hold of an experienced technician.

Honeywell Thermostat Error e43

If the Honeywell thermostat presents 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 your wide area network (WAN).

How to Fix Honeywell Thermostat Error e43

Reset the router by unplugging it and leaving it that way for a short period. The thermostat might also be disconnected if you have recently updated the password or the Wi-Fi’s SSID, which is the name you give it.

Honeywell Error Code e1

Thermostats employ sensors to detect the temperature outdoors and indoors. If a sensor malfunctions, you may see error code e1 turn up on your Honeywell smart thermostat.

How to Fix Honeywell Thermostat Error e1

A skilled technician can replace the sensor and restart the thermostat, which should take care of error code e1.

Honeywell Thermostat Error 11n

Error code 11n can appear in situations where the thermostat can’t connect to a heating or cooling unit. This can mean that the equipment itself is malfunctioning and unable to connect with the thermostat. This sometimes happens when the wiring is defective or even if the thermostat has failed.

How to Fix Honeywell Thermostat Error 11n

A professional technician can use a voltmeter to assess if there’s a faulty electrical connection. If the wiring on your existing HVAC system is bad, the technician can replace it. In situations where the thermostat itself is the issue, it should probably be replaced.

Error Code e2 for Honeywell Thermostats

If you notice error code e2 show up on your Honeywell smart thermostat, it could mean several different things. For example, one of the sensors used to detect the temperature isn’t working correctly. Other times, it means the router was disconnected from power before the thermostat finished the setup process.

How to Fix Honeywell Thermostat Error e2

In situations where the error code stems from sensor failure, a technician should troubleshoot and replace the damaged sensor. If the problem comes from disconnected power, all you'll need to do is see to it that the router stays on throughout the setup process.