4 Signs Your Gas Furnace Needs Repair Immediately

If you smell gas or a carbon monoxide (CO) alarm sounds, leave the house, call 911 or Southwest Gas from outside, and don't flip switches. Don't stop to adjust the thermostat, shut a valve or find the source. Stay outside until emergency responders say it is safe to return.

Some furnace problems need a repair appointment. Others need an evacuation first. Knowing the difference matters more than identifying the broken part.

This guide applies to gas furnaces. Many Tucson homes use heat pumps, which have no gas burners or flame sensor. Electrical hazards and loss of heat still matter in those homes, but gas-combustion advice does not describe how a heat pump works.

1. A rotten-egg smell near the furnace

A sulfur or rotten-egg odor can warn of a natural-gas leak. Treat it as a possible leak rather than trying another heating cycle to see whether the smell clears. You do not need to prove the furnace is responsible before leaving.

Do not use a phone inside, operate electrical switches or try to relight the furnace. Make the emergency call from outside, away from the building. This is not a situation for online booking or waiting for a repair callback.

A CO alarm does not detect a natural-gas leak. The absence of an alarm does not make a gas smell safe, and the absence of a smell does not rule out carbon monoxide.

2. A burning-plastic smell, sparks or smoke

Gas furnaces also use electrical parts. A hot-plastic smell, visible sparking or smoke can indicate an electrical hazard, not simply dust warming up after months without heat. Smoke or fire means leave the house and call 911 from outside.

If there is a burning odor without smoke, gas odor or a CO alarm, stop using the furnace. Turn it off at the thermostat only if you can do so safely. Do not remove panels, touch wiring or repeatedly reset a tripped breaker.

A click by itself does not diagnose bad wiring; some operating sounds are normal. A new sound paired with a burning smell or a breaker that trips is a different concern. A technician typically checks electrical connections, controls and motors to locate the fault rather than guessing from the noise.

3. A CO alarm or signs of combustion trouble

Carbon monoxide has no smell. A sounding CO alarm requires evacuation, even if the furnace seems to be heating normally. Headache, dizziness or nausea affecting people in the home can also signal possible exposure; leave and call 911 rather than trying to diagnose the furnace.

Soot around the furnace or a new booming sound at ignition warrants stopping use and arranging professional evaluation. Do not open the burner compartment to inspect the flame. A photo, sound or stain alone cannot confirm a cracked heat exchanger.

The heat exchanger separates combustion gases from the air circulated through your home. A technician typically evaluates combustion, venting and the exchanger when investigating a safety concern. The problem needs testing, not a parts recommendation based only on symptoms.

Use 10-year sealed CO alarms on every level and outside sleeping areas, following their placement and testing instructions. Alarms are a safety backup, not permission to keep running a suspect furnace.

4. The furnace stops heating altogether

No heat is not automatically a gas emergency. But a Tucson freeze can make a cold house unsafe, especially for infants, older adults and people with health conditions. Move to a safely heated place if the house cannot stay warm.

If there are no warning smells, smoke or alarms, check that the thermostat is set to heat and above room temperature. Note whether the furnace stays silent, starts then stops, or blows air without warming it. Those observations help explain the problem without dismantling anything.

Do not use a gas oven or outdoor fuel-burning equipment to heat the house. Avoid repeated restart attempts; loss of heat may mean a safety control is preventing operation.