A Honeywell smart thermostat is a great way to optimize how you use your home comfort system. But like any technology, you could sometimes run across a problem. With the digital display, Honeywell smart thermostats can display an error code that trained technicians use to understand what's wrong. Here are some of the most likely error codes you could see on your Honeywell smart thermostat.

Honeywell Thermostat Error e42

You might encounter this error code if your home’s Wi-Fi connection did not supply an IP address for the thermostat to connect with. This can happen if a router doesn't execute the Dynamic Host Configuration Protocol, or DHCP. This process automatically sends out the needed 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 is enabled for DHCP. Assuming it does, you may also have to power cycle the router and complete the initial setup process again with your thermostat. This should see to it that the DHCP is delivered and connects to your smart thermostat.

Honeywell Thermostat Error e02

Error code e02 occurs if the password for connecting to your home’s Wi-Fi router was incorrect. When this error code has appeared for 30 seconds, the thermostat’s digital display automatically transitions to the Wi-Fi setup screen so you can try the password again.

How to Fix Honeywell Thermostat Error e02

All you have to do to solve error e02 is ensure you’re typing the correct Wi-Fi password when configuring the thermostat.

Honeywell Thermostat Error 40

Error code 40 can appear 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 directed to. But this error code could also show up if power is disconnected from the outdoor unit for an extended period of time. A “High Pressure Fault” error, induced by poor airflow, can lead to this error code. And finally, you may see error code 40 if there’s an issue 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 normal operation. If you restart the thermostat and error code 40 reappears, it’s best to get a hold of an experienced technician.

Honeywell Thermostat Error e43

If a Honeywell thermostat presents error code e43, it is unable to communicate with the router, and by extension your Wi-Fi. This might 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 a short period. The thermostat may also be disconnected if you’ve recently switched the password or the Wi-Fi’s SSID, which is the name you give it.

Honeywell Thermostat Error e1

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

How to Fix Honeywell Thermostat Error e1

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

Honeywell Thermostat Error 11n

Error code 11n could appear in situations where the thermostat is unable to recognize a heating or cooling unit. This might 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 is faulty.

How to Fix Honeywell Thermostat Error 11n

A qualified technician can utilize a voltmeter to find out if there’s a bad electrical connection. When the wiring on your existing HVAC equipment is bad, the technician can replace it. In situations where the thermostat itself is the source of the error code, it will likely have to be replaced.

Honeywell Thermostat Error e2

If you notice error code e2 appear on your Honeywell smart thermostat, it can mean a few different things. In some cases, one of the sensors used to detect the temperature isn’t working correctly. In other cases, it means the router was disconnected from power before the thermostat completed the setup process.

How to Fix Honeywell Thermostat Error e2

If the error code stems from sensor failure, a technician should troubleshoot and swap out the impacted sensor. When the problem comes from disconnected power, all you'll need to do is see to it that the router stays on during the setup process.