Furnace Troubleshooting

A malfunctioning furnace can be frustrating, especially in cold weather. This guide will help you troubleshoot common furnace issues before calling a professional.

Basic Furnace Troubleshooting

Furnace troubleshooting begins with simple checks to rule out common issues. Before calling a professional, ensure:

The furnace has power and the switch is turned on.

The thermostat is set to “heat” and has working batteries.

The air filter is clean and not restricting airflow.

A clogged filter can cause heating inefficiency or even system shutdown. Check your owner’s manual for filter replacement instructions.

Gas Furnace Troubleshooting

Most U.S. homes use natural gas furnaces. These troubleshooting steps also apply to propane furnaces.

Furnace Not Turning On

Verify the thermostat has power and is set to “heat.”
Increase the temperature setting to ensure activation.
Set the fan switch to “on” or “auto.”
Check the circuit breaker or fuse box for tripped circuits.
For older models, ensure the pilot light is lit per the owner’s manual.
Confirm the gas supply is on. If you suspect a leak or smell gas, evacuate immediately and call the gas company.

Air Not Hot Enough

Inspect and replace a dirty air filter, which can restrict airflow and reduce heating efficiency.

Furnace Turns Off and On Constantly

Ensure the thermostat is correctly set to “heat” with the fan on “auto” or “on.”
A system that short cycles may be improperly sized, have a misplaced thermostat, or need servicing.
Check for clogged air filters restricting airflow.
Ensure air vents are open and unobstructed to allow proper circulation.

Noisy Furnace Operation

A whistling sound may indicate a clogged air filter.
Loud ignition sounds may result from clogged burners, requiring professional cleaning.
Whistling or rattling noises may signal loose ductwork connections.

When to Call a Professional

If your furnace still won’t turn on after these troubleshooting steps, it may require expert diagnosis and repair. Professional technicians can evaluate your entire heating system, including air conditioners, heat pumps, and air purifiers, to ensure optimal home comfort. Don’t hesitate to reach out for professional assistance.