Why Your Furnace Won’t Turn On & How to Fix It

Few things are more frustrating than a furnace that won’t turn on—especially during the cold months when you rely on it for warmth. If your heating system refuses to start, don’t panic. There are several common reasons why a furnace might fail to turn on, and in many cases, the fix is simple.

At D-N-D Services, we’ve helped homeowners in Rockwall and surrounding areas diagnose and fix furnace problems for over two decades. Below, we’ll go over the most common reasons your furnace won’t start and how to troubleshoot the issue.

Thermostat Issues

Problem:

Your thermostat controls the furnace, and if it’s not working properly, your furnace won’t turn on.

How to Fix It:

1. Check the settings – Make sure the thermostat is set to “heat” and that the temperature is set higher than the current room temperature.
2. Replace the batteries – If your thermostat runs on batteries, weak batteries could be causing the issue.
3. Reset the thermostat – Some thermostats have a reset button, or you can remove the batteries for a few minutes and reinstall them.
4. Check for loose wiring – If your thermostat isn’t responding properly, wiring issues could be the culprit.

Power Supply Issues

Problem:

Your furnace needs electricity to run, even if it’s gas-powered. A tripped circuit breaker or power issue could be stopping it from turning on.

How to Fix It:

1. Check the breaker box – Look for a tripped breaker and reset it if necessary.
2. Inspect the power switch – Your furnace has a power switch, usually located nearby. Make sure it’s turned on.
3. Look for a blown fuse – If your home has a fuse box, a blown fuse could be preventing power from reaching the furnace.

Dirty or Clogged Air Filter

Problem:

A dirty air filter restricts airflow, which can cause the furnace to overheat and shut down as a safety measure.

How to Fix It:

1. Check the filter – If it looks clogged with dust and debris, replace it with a clean filter.
2. Change filters regularly – We recommend replacing your filter every 1-3 months to keep your furnace running smoothly.

Pilot Light or Ignition Problems

Problem:

Older furnaces use a pilot light, while newer ones use electronic ignition systems. If the ignition system isn’t working, the furnace won’t turn on.

How to Fix It:

1. Check if the pilot light is out – If you have a gas furnace, follow your manufacturer’s instructions to relight the pilot light.
2. Inspect the flame sensor – A dirty flame sensor can prevent ignition. Carefully clean it with a soft cloth and reinstall it.
3. Listen for clicking sounds – If you hear clicking but the furnace doesn’t light, the ignition system may need repair.

Gas Supply Issues

Problem:

If your furnace runs on natural gas or propane, it won’t turn on if there’s an issue with the gas supply.

How to Fix It:

1. Check the gas valve – Ensure the gas supply valve to the furnace is fully open.
2. Try another gas appliance – If your stove or water heater also isn’t working, there may be a gas supply issue. Contact your gas provider.
3. Call a professional – If you smell gas, turn off the furnace immediately and call D-N-D Services or your gas company.

Blocked or Closed Vents

Problem:

Blocked or closed air vents disrupt airflow and can cause the furnace to shut down.

How to Fix It:

1. Make sure all vents are open – Check that none of your home’s vents are closed or blocked by furniture.
2. Inspect air ducts – If your home has severe duct leaks or blockages, professional duct cleaning may be needed.

Faulty Limit Switch

Problem:

The limit switch is a safety feature that shuts down the furnace if it overheats. If it’s malfunctioning, it may prevent the furnace from starting.

How to Fix It:

1. Check the air filter – A clogged filter can cause overheating, which trips the limit switch.
2. Reset the furnace – Turn the furnace off, wait 10-15 minutes, and turn it back on.
3. Call a professional – If the limit switch is faulty, D-N-D Services can replace it.

Furnace Blower Issues

Problem:

The blower distributes warm air throughout your home. If it’s not working, your furnace might not start.

How to Fix It:

1. Listen for the fan – If you don’t hear the blower running, it may be malfunctioning.
2. Check for obstructions – Dust and debris can clog the blower motor. A professional cleaning may be needed.
3. Test the capacitor – The capacitor starts the blower motor. If it’s failing, the blower won’t work. D-N-D Services can replace it.

When to Call a Professional

If you’ve checked these common issues and your furnace still won’t turn on, it’s time to call in the experts. D-N-D Services provides fast, reliable furnace repair in Rockwall and surrounding areas.

Signs You Need Professional Help:

1. You smell gas – Shut off your furnace and call for emergency service.
2. Your furnace keeps shutting off – This could indicate a serious issue.
3. You’ve tried troubleshooting, but the furnace still won’t start.
4. You hear loud banging, screeching, or rattling noises.

Prevent Future Furnace Problems

To avoid furnace breakdowns, regular maintenance is key. D-N-D Services offers professional tune-ups that include:

1. Inspecting and cleaning furnace components
2. Checking for gas leaks or carbon monoxide issues
3. Testing the thermostat and ignition system
4. Replacing dirty air filters
5. Ensuring the system runs at peak efficiency

Regular maintenance reduces breakdowns, improves efficiency, and extends your furnace’s lifespan.

Conclusion

If your furnace won’t turn on, D-N-D Services is here to help. Our NATE-certified technicians can diagnose and fix your heating system quickly and efficiently. We serve Rockwall, Rowlett, Heath, Sunnyvale, Mesquite, Garland, Greenville, Sulphur Springs, Dallas, and surrounding areas.

Don’t get left in the cold! Call us today for fast, reliable furnace repair and maintenance. Your comfort is our priority!