NYC Metro Area’s HVACR Blog

Commercial HVAC, Residential HVAC

Furnace Blowing Cold Air? 13 Common Causes.


furnace blowing cold

Here in the New York City area, we’re all pretty tired of the cold weather by now. No matter how you travel to work, whether it’s by bus, car or train, your commute probably ends with a cold walk in the icy wind. When you get to your destination, you expect to walk into a toasty warm space. The last thing you want to find is that the furnace is not heating. Even worse, the furnace is blowing cold air!

Even if your furnace is fairly new, things can go wrong that cause this unpleasant surprise. In some cases, you may be able to fix the problem yourself. But you need to know when to call in the furnace repair pros so you don’t have to spend unnecessary time in the cold and interrupt your business. You also don’t want to risk frozen pipes.

Read on to learn the 13 most common reasons for your furnace blowing cold air and when to call for a furnace repair.

13 reasons your furnace is blowing cold air

1. Incorrect thermostat setting.

Do you have thermostat wars going on in your office? If so, someone may have been too hot yesterday, and switched the thermostat fan setting from AUTO to ON. This means the fan will run continuously without providing heat. Change the setting back to AUTO, and you’ll have heat again. Count your blessings that this time you avoided an expensive furnace repair.

2. Other thermostat issues.

Here’s another possible DIY fix for your heater blowing cold air. Have you installed a new thermostat lately? If you did it yourself instead of calling a professional, you may have chosen a thermostat that’s not compatible with your heating system. Consult an HVAC expert for advice. If you’ve had the thermostat for a while, the battery might be low. Try changing the batteries.

2. Empty oil tank.

If you have an oil-fired furnace, you may be out of fuel. If so, your blower may keep circulating cold air even after the burners fail to light and produce heat.

3. Problem with computerized controls.

If you have a newer furnace with an electronic control panel, you may need to reset the system. Try turning the furnace off via the power switch. Wait a few minutes, then restart. This is similar to rebooting your computer to fix a software glitch. If the furnace still blows cold air, call in a professional.

4. Overheated furnace.

Have you changed your air filter lately? If not, the compromised air flow can cause your furnace to overheat, shutting down the burner. That’s why the furnace is not blowing hot air. Try changing the air filter and restarting the furnace.

5. Extinguished pilot light.

If you have an older furnace with a continuous pilot light, the pilot may have gone out. This could happen from a gust of air caused by someone working near the furnace. If you know how and you’re comfortable doing it, you can try to relight the pilot yourself. If not, call a professional.

6. Valve problem.

If the pilot won’t light at all, you may have a faulty gas valve. Or, if your system has not been cleaned in a while, a valve could be stuck due to dirt and debris. Have your system cleaned and checked by an HVAC professional.

7. Faulty thermocouple. 

If you do manage to relight the pilot but it keeps going out, a faulty thermocouple is likely causing your furnace to blow cold air. The thermocouple is a sensor that controls the gas valve and ignition. This is usually a simple fix, but you’ll need to call a technician to adjust or replace it.

8. Clogged oil filter.

If you have an oil-fired furnace, its filter can become clogged with dirt and debris, just like an air filter on a gas-fired system. When the filter is clogged, ignition can be affected and the result is your heating not blowing hot air. If you know how, you can clean or replace the filter yourself, but it’s messy and not as easy as an air filter so you may want to leave this job to the pros.

9. Faulty electronic ignition.

If you have a newer furnace with an electronic ignition, such as an intermittent pilot or a hot surface ignition, your system may need adjustments or replacement of failed parts. This problem requires a visit from your HVAC repair technician.

10. Leaking ducts.

Your furnace blowing cold air could be caused by hot air escaping through holes in the duct work that carries the heat throughout your building. Have an expert inspect your ducts along with the furnace.

11. Compromised flame sensor.

If your furnace starts blowing warm but then quickly turns cold, the flame sensor may need attention. A flame sensor that’s covered with grime or worn out can cause the burner to keep shutting off. You’ll need a visit from an HVAC professional to make this furnace repair.

12. Dirty oil or gas burner.

If the furnace burner itself is neglected, accumulated dust and grime can cause trouble igniting. Have your system professionally cleaned to take care of this problem.

Regular maintenance can prevent HVAC problems like your furnace blowing cold air

Many of the causes of furnace problems can be prevented with regularly-scheduled cleaning and maintenance. If you haven’t done that yet this winter, call in an HVAC service expert to keep your system in top shape and prevent unexpected failures.

Afraid it’s too expensive? The best service providers can customize a plan for your needs and your budget. Learn more from our free guide: HVAC Preventative Maintenance Contracts: How to Find the Right One for Your HVAC Infrastructure.

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