Furnace Troubleshooting Guide
Diagnose common furnace problems yourself. Learn what you can safely fix at home and when it's time to call a professional HVAC technician.
Need Professional Help?
Can't fix it yourself? Our NATE-certified techs will diagnose it.
First-time customers save $50
100% credited toward any repair
Safety First
These situations require immediate action—not DIY troubleshooting
Smell Gas?
Leave immediately. Don't flip switches or use phones inside. Call gas company from outside.
CO Detector Alarming?
Evacuate all people and pets immediately. Call 911 from outside the home.
Yellow/Orange Flame?
May indicate carbon monoxide production. Turn off furnace and call for service.
Burning Smell?
Could be dust (normal at startup) or electrical issue. If persistent, shut down and call.
What's Your Furnace Doing?
Select your symptom for causes and solutions
Furnace Blowing Cold Air
Heat pump or burner issues may be preventing warm air production
Furnace Short Cycling
Turning on and off frequently wastes energy and damages components
Furnace Making Noise
Banging, squealing, or grinding can indicate serious problems
Yellow or Flickering Flame
May indicate incomplete combustion or carbon monoxide risk
High Energy Bills
Sudden increases often indicate efficiency problems
Furnace Won't Start
No heat at all—could be ignitor, thermostat, or control board
DIY Troubleshooting Checklist
Safe steps you can try before calling a pro
Check the Thermostat
Ensure it's set to HEAT, temperature is higher than current room temp, and batteries are fresh.
Inspect the Air Filter
A clogged filter is the #1 cause of furnace problems. If you can't see light through it, replace it.
Check the Circuit Breaker
Find your furnace breaker and ensure it hasn't tripped.
Verify the Furnace Switch
There's usually a light switch on or near the furnace. Ensure it's ON.
Check All Vents
Ensure all supply vents and return air grilles are open and unobstructed.
Look for Error Codes
Most furnaces have a small window showing LED lights. Note any blinking patterns.
Still Not Working?
Our NATE-certified technicians can diagnose any furnace problem.
When to Call a Professional
These signs require expert diagnosis—don't risk further damage
Gas smell or suspected leak
Evacuate & call gas company
Carbon monoxide detector alarming
Leave immediately, call 911
Yellow or flickering pilot flame
Indicates CO risk
Furnace over 15 years old with issues
May need replacement assessment
Repeated circuit breaker trips
Electrical hazard
Grinding or banging noises
Stop using immediately
No heat despite troubleshooting
Needs professional diagnosis
Visible damage to components
Don't attempt DIY repair
Ready for Expert Help?
$79 diagnostic for new customers • Credited toward repairs
Frequently Asked Questions
Frequently Asked Questions
Get answers to common questions about our services
Need Help Now?
Same-day diagnostic service available in Nassau County
(516) 259-1191Furnace Brands We Troubleshoot & Repair
NATE-certified technicians with manufacturer diagnostic tools
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Furnace Troubleshooting Throughout Nassau County
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