HVAC Won't Turn On: Basic Troubleshooting Steps

Your HVAC system won't turn on. Before you call for service, check these basics—you might save a service call.

First: Check the Obvious

Thermostat - Is it set to HEAT or COOL (as appropriate)? - Is the temperature set to actually call for heating or cooling? - Are batteries dead (if battery-powered)? - Is the display working?

Power - Check the breaker box—did a breaker trip? - Is the HVAC disconnect switch (near the indoor or outdoor unit) in the ON position? - Did a fuse blow? (older systems may have fuses)

Filter An extremely dirty filter can cause the system to shut down on safety limits. Replace it and try again.

System-Specific Checks

Furnace/Heating - Check for a pilot light (older systems) or verify the igniter clicks - Look for a blinking LED on the control board—this indicates error codes - Make sure the furnace door is fully closed (safety switch prevents operation when open) - Check the gas valve is on

Air Conditioning - Look for ice on the indoor unit (indicates freeze-up—let it thaw) - Check the outdoor unit—is the fan or compressor running? - Listen for the compressor trying to start (clicking or humming)

When to Call a Professional

These require service: - Blown fuses that blow again when replaced - Blinking error codes - Burning smells - Unusual sounds when trying to start - Visible damage to components - Gas smells (call the gas company first, then HVAC service)

After trying the basics If basic troubleshooting doesn't reveal an obvious issue, it's time for professional diagnosis. Attempting to repair electrical or gas components without training is dangerous.

Before the Technician Arrives

Note: - What happens when you try to turn on the system - Any unusual sounds, smells, or behaviors - When the problem started - Any recent changes (power outages, home renovations, etc.)

This information helps the technician diagnose the issue faster.