my ecobee is making a faint but constant clicking sound from inside the unit, is this normal?

Diagnosis

A faint, rhythmic clicking sound emanating from the ecobee SmartThermostat Enhanced is typically the sound of the mechanical relays engaging and disengaging. Unlike solid-state switches, the relays in the Enhanced model physically move a metal contact to complete the 24V circuit to your HVAC equipment. When the thermostat "calls" for heat, cooling, or fan activity, the electromagnetic coil inside the relay snaps the switch shut, creating that distinct clicking noise. If the clicking occurs only when the system is transitioning from "Idle" to "Cooling" or "Heating," it is a sign of normal operation. However, if you hear a rapid, constant "chattering" (a series of fast clicks) or a persistent click while the screen indicates the system is off, you are experiencing "short-cycling" or a relay failure. This happens when the thermostat is rapidly toggling the circuit due to a faulty temperature sensor, a poorly placed unit causing a draft (ghosting), or a failing internal capacitor that cannot maintain a steady voltage to the relay coil. To confirm, check the "Equipment Status" on the device screen; if the status is flipping between "Idle" and "Heating/Cooling" every few seconds, the relay is reacting to a software or sensor trigger.

How to Fix It

If the clicking is abnormal (constant or rapid), follow these steps to isolate and resolve the issue:

1. Perform a Hard Power Cycle: Turn off the breaker to your HVAC system for exactly 60 seconds. This clears the volatile memory of the SmartThermostat Enhanced and resets any stuck relay states. Restore power and observe if the clicking persists.
2. Check for "Drafting" (The Hole-in-the-Wall Issue): Remove the thermostat from the wall plate. Look at the hole where the wires emerge from the drywall. If there is a large gap, cold or warm air from inside the wall can blow directly onto the internal sensors, causing the thermostat to click on and off rapidly. Seal this hole using plumbers putty, electrical tape, or expanding foam.
3. Verify C-Wire Voltage: Ensure your C-wire is providing a steady 24VAC. If the voltage drops below 20V, the relay coil may not have enough power to hold the contact closed, leading to a constant "chattering" click. Use a multimeter to test the voltage between the R and C terminals on the backplate.
4. Adjust Temperature Differential: Go to Main Menu > Settings > Installation Settings > Thresholds. Increase the "Heat Differential Temp" or "Cool Differential Temp" to 2.0°F. This prevents the system from clicking on and off too frequently when the room temperature hovers exactly at the set point.

If That Didn't Work

• Inspect for Wire Frays: Pull the thermostat off the wall and examine the copper leads. If a strand of wire from the R-terminal is touching the C-terminal or the chassis, it can create an intermittent short that triggers the relay. Trim any excess wire and re-insert them firmly into the push-terminals.
• Disable "Smart Recovery": Sometimes the "Smart Recovery" feature triggers the system to start heating/cooling long before the scheduled time. If the clicking happens at odd hours, disable this in the Settings menu to see if the behavior stops.
• Test with a Different Power Source: If you are using a Power Extender Kit (PEK), the clicking may be caused by a voltage drop across the adapter. Bypass the PEK by running a dedicated 18/5 wire to the thermostat to determine if the relay is failing or if the power delivery is unstable.
• Request a Warranty Replacement: If the clicking is accompanied by a failure to trigger the HVAC equipment (e.g., you hear the click but the AC doesn't start), the internal relay has likely suffered a mechanical failure. Since the Enhanced model is a premium unit, contact ecobee for a replacement if the device is within its warranty period.

Heads Up

• Avoid High-Voltage Wiring: Never connect 120V or 240V lines to the ecobee; this will instantly fry the relays and may cause a permanent buzzing or clicking sound before total failure.
• Firmware Updates: Keep your device updated. ecobee occasionally releases firmware patches that optimize the "cycling" logic to reduce wear and tear on the mechanical relays.
• Sensor Calibration: If you have remote sensors, ensure the thermostat is averaging the temperature correctly. A single malfunctioning remote sensor can cause the main unit to click repeatedly as it tries to resolve conflicting temperature data.
• Clean the Backplate: Dust accumulation inside the backplate terminals can cause micro-arcs. Use a can of compressed air to blow out the terminals every few years to ensure a clean electrical connection.