Ecobee Thermostat Error Code 4: How to Fix It

Q: What does Ecobee error code 4 mean?

Error code 4 means the C (common) wire is not detected at the thermostat and no Power Extender Kit (PEK) is installed. This prevents the thermostat from receiving continuous power.

Q: Can I use Ecobee without a C wire?

Yes, but you must install the included Power Extender Kit (PEK) to provide a virtual C wire. Without it, the thermostat may experience power issues.

Q: How do I know if I have a C wire?

Remove your thermostat and look for a wire connected to a terminal labeled 'C'. Also check the furnace control board for a wire on the C terminal. Often, a blue or black wire is used for C.

Q: What if my C wire is not connected at the furnace?

You can connect an unused wire (often blue) to the C terminal on both the furnace and thermostat. If no wire is available, install the PEK or use a 24V power adapter.

Q: Why does my Ecobee keep restarting after error code 4?

Intermittent power loss due to a missing or loose C wire can cause the thermostat to restart. Ensuring a solid C connection or installing the PEK resolves this.

Abstract

Ecobee error code 4 indicates that the C (common) wire is not detected at the thermostat, and there is no Power Extender Kit (PEK) installed. This means your thermostat may not receive continuous power, causing issues like battery drain or random reboots. This guide will help you diagnose and fix the problem, ensuring your thermostat operates reliably.