Your Ecobee thermostat cooling works perfectly, but when winter arrives and you switch to heat mode, nothing happens. This frustrating issue typically points to specific heating system problems rather than a faulty thermostat, and you can often fix it yourself within 30 minutes.
Step-by-Step Fixes
Step 1: Check Your Ecobee Display Settings
Navigate to your thermostat’s main screen and tap the gear icon for settings. Select “Installation Settings” then “Equipment” to verify your heating system shows as configured. If you see “Heat: Not Configured” or similar, your Ecobee isn’t recognizing your heating equipment. This quick check takes under 60 seconds and reveals whether you’re dealing with a settings issue or hardware problem.
Step 2: Test the Furnace Power Switch
Locate your furnace’s power switch, which looks like a regular light switch mounted on or near the unit. Many homeowners accidentally flip this switch while storing items or cleaning. Turn it off, wait 30 seconds, then flip it back on. You should hear your furnace’s fan start briefly. If nothing happens, check your home’s electrical panel for a tripped breaker labeled “Furnace” or “HVAC.”
Step 3: Inspect and Replace Your Furnace Filter
Pull out your furnace filter and hold it up to a light. If you can’t see light through it, the filter is clogged and blocking airflow. Modern furnaces shut down when airflow drops too low, protecting the heat exchanger from damage. Replace with a new filter matching the size printed on the old one’s frame. Standard sizes include 16x25x1 or 20x25x1 inches.
Step 4: Verify Ecobee Wiring Connections
Turn off power at your breaker box before removing your Ecobee from the wall. Check that the W1 wire (usually white) connects firmly to the W1 terminal. This wire controls your heating system. Also verify the C wire (typically blue) sits securely in its terminal, as this provides constant power. Loose connections cause intermittent heating failures while leaving cooling unaffected.
Step 5: Run Ecobee’s Built-in Diagnostics
Access “Installation Settings” then “Test Equipment” on your thermostat. Select “Test Heating” and listen for your furnace to start. If you hear clicking but no ignition, your furnace receives the signal but can’t start. No clicking suggests a wiring issue between your Ecobee and furnace. Document any error codes displayed for troubleshooting.
Step 6: Reset Your Ecobee to Factory Settings
When other steps fail, perform a full reset. Go to “Settings,” then “Reset,” and choose “Reset All Settings.” You’ll need to reconfigure your schedule and preferences, but this clears any corrupted data preventing heat operation. Take photos of your current settings first to speed up reconfiguration.
Likely Causes
Cause #1: Blown Furnace Fuse
Your furnace contains a 3-amp or 5-amp automotive-style fuse on its control board. When this fuse blows, your furnace won’t respond to heat calls while your AC continues working normally since it uses different circuits. Remove your furnace’s front panel and locate the small purple or orange fuse near the board’s edge. Pull it out and check if the metal strip inside is broken. Replace with an identical amp rating fuse from any auto parts store.
Cause #2: Dirty Flame Sensor
Gas furnaces use a flame sensor rod to verify safe combustion. Carbon buildup on this metal rod prevents proper flame detection, causing your furnace to shut down seconds after igniting. Find the thin metal rod extending into the burner area, remove its single screw, and gently clean with fine steel wool or emery cloth. This five-minute fix resolves heating issues in roughly 30% of cases where cooling still works.
Cause #3: Incorrect Ecobee Configuration
Your Ecobee needs proper system configuration to send correct signals. If someone selected “Heat Pump” instead of “Conventional” during setup, your furnace won’t receive proper commands. Access “Installation Settings” and verify your system type matches your actual equipment. Conventional systems use gas or oil furnaces, while heat pumps look like large AC units that provide both heating and cooling.
When to Call Expert Help
Contact an HVAC technician when you smell gas near your furnace, see error codes you can’t resolve, or hear unusual grinding or squealing sounds during operation. Professional help is ideal for electrical work beyond basic wire checking, especially if you’re uncomfortable working near 240-volt circuits. Most reputable companies charge between $89-150 for diagnostic visits in 2025, and they’ll credit this toward repairs if you proceed with their service.
Copy-Paste Prompt for AI Help
“My Ecobee thermostat works fine for cooling but won’t turn on heat. I’ve checked the furnace power switch and replaced the filter. The display shows heat mode selected but the furnace never starts. My system is a [insert: gas/oil/electric] furnace installed in [year]. When I run test mode, I [hear clicking/hear nothing/get error code]. What specific troubleshooting steps should I try next?”