Common Reasons a Furnace Isn't Pushing Out Air

From something as simple as the unit being unplugged to a power outage to an issue requiring an HVAC tech.

Furnaces not blowing hot air are among the few winter issues to draw as much ire. However, homeowners quickly address most cases, even without electrical training. From something as simple as the unit being unplugged to a power outage to an issue requiring an HVAC tech.

Here are some common reasons a furnace isn't pushing out hot air:

Thermostat problems

Thermostats control the HVAC system; if they malfunction, the air conditioner and heater also stop working. So checking this device should be the main priority. For example, it may have run out of battery life, or the thermostat is set to "off" and not heat, preventing the furnace from pumping out air. Replacing the battery or switching the fan setting to heat can help restore the furnace to working order.

A poorly installed thermostat can also prevent the furnace from operating correctly. In this case, homeowners should call a professional electrician or HVAC specialist for assistance.

Clogged filters

Furnace filters keep unwanted debris out but need cleaning to ensure air flows without restriction. Doing so tends to help the furnace push hot air out again. Some furnace models have a system that prevents operation if a filter is too dirty.

Should a filter appear caked with mud or soil, it's time to clean or replace it. Clogged filters can cause overheating, as there's no airflow to bring the heat out. Once a fresh filter replaces the old one, the furnace should return to normal.

Burner problems

Another component that's vulnerable to grime and dirt is the burner. Clogged burners will only let the cool air blow or may even cause the system to shut down completely, so the solution is to clean it. While homeowners can learn how the process goes, a professional tends to do a better job and even knows how to reach awkward areas.

Flame sensor issues

Flame sensors, like all parts, will eventually wear out or become coated with dust. While a defective flame sensor can cause the burner to shut down, the fan may keep running, bringing only cold air into the house. A replacement or cleaning by a professional HVAC technician should address this issue.

Dirty gas valve

The gas valve can become dirty if it hasn't been cleaned for a while. Clogged valves will usually result in the furnace malfunctioning. In other cases, the valve has deteriorated and needs a replacement. A bad valve results in furnaces only blowing cold air.

Broken pilot light

Similar to gas stoves, a gas-powered furnace has a pilot light. When extinguished, the furnace won't ignite the fuel and produce heat. Old furnaces may have leaks that let drafts put this small flame out. New technology may cause the entire system to shut down for safety, providing no air. Homeowners can learn how to relight a pilot light and get warm air pumping again.

Get the furnace blowing the right way

While untrained homeowners can address many problems with the furnace, persistent issues require professional attention. Reach out to a reputable HVAC company for assistance, as the pros have all the experience and equipment to fix the problem and get the furnace working again.


Fix My Air DFW of Fort Worth specializes in residential and commercial HVAC services including routine maintenance, installation, and repair. All makes/models. Call us at (817)839-3511.

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