ecobee3 lite Thermostat Not Heating or Cooling

Common Causes

When your ecobee3 lite thermostat is not heating or cooling your home, the issue may be related to the thermostat itself, the wiring, or your HVAC equipment. Common causes include:

• Thermostat set to the wrong mode (heat, cool, auto, or off)
• Temperature differential too small to trigger the HVAC system
• Wiring issue at the thermostat or furnace control board
• Power Extender Kit (PEK) malfunction
• HVAC system in safety lockout
• Compressor protection timer preventing immediate cooling
• HVAC equipment failure unrelated to the thermostat
• Air filter clogged, restricting airflow and triggering safety shutoffs

Step 1: Check the Thermostat Mode

On the ecobee3 lite touchscreen, verify the current mode. Tap the system mode icon and make sure it is set correctly:

• Heat — for heating only
• Cool — for cooling only
• Auto — to switch between heating and cooling as needed
• Off — the HVAC system will not run

If the mode is set to Off, the thermostat will not call for heating or cooling regardless of the temperature setting.

Step 2: Verify the Set Temperature

The HVAC system will only activate when the current temperature differs enough from the set temperature. The default temperature differential on ecobee is typically 0.5 degrees Fahrenheit. If the room temperature is very close to the setpoint, the system may not engage. Try adjusting the set temperature three to five degrees above (for heating) or below (for cooling) the current room temperature and wait five minutes to see if the system activates.

Step 3: Look for the "Calling" Indicator

When the ecobee3 lite is actively requesting heating or cooling, the screen will display "Heating to" or "Cooling to" followed by the target temperature. If you see this message but feel no warm or cool air from the vents, the problem is with the HVAC equipment, not the thermostat. If you do not see this message even when the temperature is far from the setpoint, the thermostat configuration or wiring may be the issue.

Step 4: Check the Compressor Protection Timer

The ecobee3 lite has a built-in compressor protection timer that prevents the air conditioner compressor from short-cycling. After the cooling system turns off, there is a minimum five-minute delay before it can turn on again. If you recently changed settings, wait at least five minutes before concluding that cooling is not working.

Step 5: Inspect the Wiring

1. Turn off the HVAC breaker.
2. Remove the ecobee3 lite from the wall plate.
3. Verify all wires are securely connected to the correct terminals.
4. Check specifically that the W wire (heating) and Y wire (cooling) are present and firmly connected.
5. If using a Power Extender Kit, inspect the PEK connections at the furnace control board as well.
6. Reattach the thermostat and restore power.

Step 6: Check the Air Filter

A severely clogged air filter can restrict airflow enough to trigger high-limit safety switches on your furnace, causing it to shut down and refuse to restart until the issue is resolved. Locate your HVAC air filter (usually in the return air duct or at the furnace) and check its condition. If the filter is dirty or clogged, replace it with a new one of the same size. After replacing the filter, reset the HVAC breaker to clear any safety lockout.

Step 7: Check for HVAC Equipment Errors

Open the furnace or air handler panel and look for a blinking LED on the control board. Most HVAC systems use blink codes to indicate specific errors, such as failed ignition, flame sensor issues, or pressure switch problems. Refer to your HVAC system's manual or the chart usually printed inside the panel door for error code meanings.

Step 8: Reset the HVAC System

1. Turn off the HVAC breaker at your electrical panel.
2. Wait 60 seconds.
3. Turn the breaker back on.
4. Set the ecobee3 lite to call for heating or cooling and wait five minutes for the system to respond.

This power cycle clears most safety lockouts on the HVAC equipment.

Step 9: Test with a Direct Call

To determine definitively whether the thermostat or the HVAC equipment is the problem, you can perform a direct test. On the ecobee3 lite, go to Main Menu, then Settings, then Installation Settings, then Equipment, then Test Equipment. Run the heating and cooling tests individually. If the HVAC system does not respond during the test, the issue is with the equipment or wiring, not the thermostat settings.

When to Contact a Professional

If the thermostat is correctly calling for heating or cooling but the HVAC system does not respond, you likely need an HVAC technician to diagnose and repair the equipment. Common issues include failed ignitors, burned-out capacitors, low refrigerant, or faulty control boards. For thermostat-specific problems, contact ecobee Support.