Diagnose HVAC Blowing Air Without Heat

Cost Savings

Checklist Tasks

• Set thermostat to heat and raise 5°F to start the heating cycle.
• Check thermostat batteries and wiring to rule out signal or power issues.
• Confirm furnace power switch and breaker are on and supplying electricity.
• Open furnace panel and check diagnostic LED codes for fault indicators.
• Check furnace filter for blockages that cause burner or safety shutdown.
• Listen for igniter clicking or glowing to confirm ignition is starting.
• Smell near the furnace for gas odors that signal ignition or valve issues.
• Check that gas shutoff valve is open and supply line is intact.
• Examine flame sensor for soot or corrosion and clean if needed.
• Inspect exhaust vent for blockages or ice triggering safety switches.
• Reset limit switches only after correcting the underlying fault.
• Test system after each step to isolate the problem before calling a pro.