A Honeywell smart thermostat is an easy way to optimize how you use your HVAC system. But like any technology, you might sometimes run across a problem. With a digital display, Honeywell smart thermostats can provide an error code that certified technicians can use to get a better sense of what's going on. Here are several of the most likely error codes you could see on your Honeywell smart thermostat.

Error Code e42 for Honeywell Thermostats

You might see this error code when your home’s Wi-Fi connection did not supply an IP address for the thermostat to connect with. This can occur if a router doesn't complete the Dynamic Host Configuration Protocol, or DHCP. This function automatically sends out the necessary IP address for your thermostat to link up.

How to Fix Honeywell Thermostat Error e42

You can clear error code e42 by confirming that your router can complete the DHCP. When it does, you may also have to power cycle the router and repeat the initial setup process with your thermostat. This should ensure the DHCP is delivered and connects to the smart thermostat.

Honeywell Error Code e02

Error code e02 occurs when the password for communicating with your home’s Wi-Fi router was incorrect. Once this error code appears for 30 seconds, the thermostat’s digital display automatically transitions to the Wi-Fi setup screen so you can try to enter the password again.

How to Fix Honeywell Thermostat Error e02

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

Honeywell Error Code 40

Error code 40 can pop up when the thermostat is alerted that a heat pump or air conditioner’s monitoring system has detected a malfunction. Most often, this occurs if the compressor isn’t working despite being instructed to. But this error code may also appear if power is disconnected from the outdoor unit for an extended period of time. A “High Pressure Fault” error, caused by blocked airflow, can display this error code. And finally, you might encounter error code 40 if there’s a problem 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 normal 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 displays error code e43, it can’t communicate with the router, and by extension your Wi-Fi. This could 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

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

Honeywell Error Code e1

Thermostats use sensors to detect the temperature outdoors and indoors. If a sensor fails, you might notice error code e1 show up on your Honeywell smart thermostat.

How to Fix Honeywell Thermostat Error e1

A skilled technician can swap out the sensor and reboot the thermostat, which should take care of error code e1.

Error Code 11n for Honeywell Thermostats

Error code 11n may appear if the thermostat is unable to 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 qualified technician can use a voltmeter to determine if there’s a bad electrical connection. When the wiring on your existing HVAC equipment is bad, the technician can replace it. When the thermostat itself is the issue, it should probably be replaced.

Error Code e2 for Honeywell Thermostats

If you see error code e2 appear on your Honeywell smart thermostat, it might mean a couple of different things. Sometimes, one of the sensors used to detect the temperature isn’t functioning like it should. Other times, it means the router was disconnected from its power source before the thermostat completed the setup process.

How to Fix Honeywell Thermostat Error e2

In situations where the error code is a result of sensor failure, a technician can troubleshoot and replace the impacted sensor. If the problem comes from disconnected power, all you have to do is see to it that the router remains on over the course of the setup process.