10 Most Common Furnace Problems (and Noises) and How to Fix Them

Is your furnace blowing cold air, making banging noises, or refusing to turn on? These are common issues that can often be fixed without a service call—especially when you know what to look for and where to get the right parts.

Below are the 10 most common furnace problems and furnace noises, what causes them, and how to fix them—so you can stay warm and worry-free all season.

1. Furnace Won’t Turn On

Likely Causes:

• Tripped breaker or blown fuse
• Faulty thermostat
• Ignition control failure

DIY Fix: Check the circuit breaker and ensure the thermostat is set to “heat” and the batteries are fresh. If the furnace still won’t respond, the ignition control board or limit switch might need replacing.

2. Furnace Blowing Cold Air

Common Problems:

• Dirty air filter
• Pilot light out
• Faulty flame sensor

DIY Fix: Check the air filter and replace if clogged. Relight the pilot if it’s gone out (for older models). Clean or replace the flame sensor if it’s dirty or corroded.

3. Strange Banging or Popping Noises

Possible Causes:

• Dirty burners
• Expanding ducts
• Delayed ignition

DIY Fix: Clean the burners to prevent delayed ignition. Inspect ductwork for expansion noise and tighten any loose fittings. If the noise persists, the ignition system may need professional inspection.

4. Furnace Turns On and Off Frequently (Short Cycling)

Likely Causes:

• Clogged air filter
• Improper thermostat setting
• Faulty flame sensor or limit switch

DIY Fix: Replace the air filter and check thermostat settings. Clean or replace the flame sensor and test the limit switch for continuity.

5. Furnace Runs Constantly

Possible Issues:

• Thermostat stuck in “on” mode
• Faulty limit switch
• Blower motor issues

DIY Fix: Make sure the thermostat fan setting is on “auto,” not “on.” If the fan still runs nonstop, the limit switch or blower relay may be stuck and need replacing.

6. Unusual Squealing or Screeching Sounds

Common Problems:

• Worn blower belt
• Failing motor bearings
• Loose blower wheel

DIY Fix: Inspect the blower belt for wear or slack. Lubricate or replace motor bearings if needed, and tighten or replace the blower wheel.

7. Pilot Light Won’t Stay Lit

Likely Causes:

• Dirty thermocouple
• Faulty gas valve
• Drafts in the furnace room

DIY Fix: Clean the thermocouple gently with steel wool. If it still won’t stay lit, test the gas valve and inspect the furnace for drafts that could be blowing out the flame.

8. Weak or No Airflow from Vents

Possible Issues:

• Dirty filter or blower
• Blocked ductwork
• Failing blower motor

DIY Fix: Replace the filter, clean the blower fan, and check ducts for obstructions. If airflow is still poor, the blower motor might be failing and need replacement.

9. Burning Smell When Furnace Runs

Top Causes:

• Dust on heating elements
• Clogged filter
• Overheating components

DIY Fix: A burning smell during the first use of the season is normal—dust is burning off. If the smell lingers, replace the filter and inspect for any melted wires or components.

10. Thermostat Not Responding

Common Reasons:

• Dead batteries
• Loose wiring
• Faulty thermostat

DIY Fix: Replace the thermostat batteries, check for loose wire connections, and if unresponsive, consider upgrading to a new programmable thermostat.

Furnace issues can seem intimidating—but many problems are fixable with simple diagnostics, the right tools, and genuine replacement parts. Whether you need a new flame sensor, blower motor, or limit switch, Reliable Parts has you covered with fast shipping and expert support.