Is your heater blowing cold air? Don’t stay cold and uncomfortable – try out these troubleshooting tips to solve the problem.

Check Your Thermostat

Even something as simple as changing your thermostat setting can cause your heater to blow cold air. If the setting is set to “ON” instead of “AUTO,” this will cause the furnace’s fan to run continuously, even when the system isn’t working to produce heat. Outside of a heating cycle, your furnace could be blowing cold air because of this setting mistake.

Luckily, the fix is as simple as going to your thermostat and checking the fan setting. Ensure the setting is set to “AUTO” and your heater should only run the fan during a heating cycle and not push cold air through your vents in between.

Replace Your Filter

Your air filter is a crucial component in your HVAC system. Not only does it help keep your indoor air healthy, but it also keeps your heater working properly.

Over time, your filter will get dirty from doing its job. When your air filter is covered in dust, grime, and dirt, it will block airflow through your system. This restriction of airflow can cause the temperature to rise inside your furnace, forcing the limit switch to shut down the heating cycle. Replace the dirty filter with a new one, and the furnace should go back to blowing hot air after it has cooled down.

Look for Water

Heating systems have condensate lines that move condensation and water away from the heater. When water accumulates around the heater, it means a line has been clogged with dust, dirt, mold, or other debris. The heater will then shut down as a safety measure, but the fan will continue to run unheated air.

If you see dampness or water around your heater, you can bet on a clogged condensate line. In this case, you’ll need to contact an HVAC professional to help you out. Clearing a condensate line can be tricky, and a professional will be able to do it easily and inspect the rest of your system to ensure it’s working properly.

Check Gas Valve

Many heating systems run on gas to generate heat. However, if the gas supply is inefficient, the furnace deactivates as a safety measure, thus blowing out cold air. You could have insufficient fuel due to a severed or accidentally shut-off gas line or an empty tank. It’s also possible that your furnace has an issue with a faulty ignition.

In this case, the first step is to simply check that the gas valve is turned on by ensuring the valve lever is parallel with the gas supply pipe. If the gas valve is on and the heater is still not supplying warm air, it’s time to call in a professional.


Still haven’t found the fix for your heater blowing cold air? It could be that it overheated. When your heater overheats, the system will be shut down to prevent a fire, carbon monoxide leak, or an explosion. Cold air might blow from the vent temporarily until the entire system shuts off.

As we mentioned above, a dirty filter can cause the system to overheat. But that’s not the only reason. It can also be due to a mechanical failure. A number of components and processes might cause this, like a faulty fan limit switch or a cracked furnace heat exchange. This is why we recommend preventative maintenance because, with routine inspections and cleanings, you’ll catch these malfunctioning parts before a breakdown happens.

Ductwork is Leaking

Most HVAC components begin to falter with age. And your ductwork is no exception. Over time, your ductwork can form leaks, cracks, and other damage that can cause warm air to escape. So once the air reaches your living room or bedroom, it doesn’t feel warm.

Leaks can be difficult to locate on your own, so that’s when a professional comes in. They’ll be able to inspect your ductwork and perform repairs to correct the issue and get you back to having a toasty, warm home.

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Don’t put up with a malfunctioning heater anymore, and get back to comfort with Comfort World Air Conditioning & Heating!

Comfort World is Here for Your Heating Needs

A heater blowing cold air is a true nuisance. Don’t put up with it anymore, and get back to comfort with Comfort World Air Conditioning & Heating! Our expert team can provide dependable heater repair, maintenance, and installation services. We also offer other HVAC services, such as air duct repair and replacement and AC repair and replacement. We’ve been bringing comfort to the valley for over 30 years, so you can count on us to get the job done right. Our highly trained technicians in Scottsdale, Arizona, want to bring a little more comfort to your world!