My Heil Furnace Is Blowing Cold Air Even if the Unit Is Off

Fan Switch On

• The simplest solution to this problem involves the position of the fan switch. Whether your gas burners are lit or not, the blower fan can be turned on by setting the fan switch to the “on” position as opposed to the automatic setting that makes it blow only when the heat is being produced. This results in a draft of cooler air coming from the vents throughout the house. Some people prefer this setting to help even out the temperatures in their homes, but if you wish for the air to blow only when it is warm, you must set this switch to automatic to make it stop.

Gas Valve

• The gas valve is the place where natural gas or propane flows into the system to provide the burners with fuel. These parts sometimes go bad and might not permit the gas to enter the system. A bad gas valve could have varying effects on the system, and a constantly running system that blows cold air is one of them. This is not a do-it-yourself project for someone without experience. It should be handled by a professional technician accustomed to dealing with gas appliances.

Wiring

• Electrical wiring issues can be serious problems for homeowners, no matter where they occur. The furnace wiring is no different. Bad wiring can cause the appliance to perform in all sorts of inconsistent ways, ranging from tripped breakers to complete failure, as well as constant running. Wiring issues could be the cause of the blower running all the time, even when you try to turn off the power at the thermostat. This is a job for an electrician or someone who specializes in electrical installations for HVAC systems.

Shut It Down

• Unless you find that the issue is simply the fan switch position, you should shut down all power to the Heil furnace before attempting to repair it. Even if you are awaiting the arrival of a repair technician, you should cut the power to the system at the circuit breaker as a precaution. Electrical problems are shock and fire hazards.

Other Things to Check

• As part of your investigation into the cause of the problem, check the easy solutions first. Make sure the thermostat is set properly on “heat” instead of “cool” and that the thermostat is working properly and is not in need of batteries if it is a digital model. Weak or dead batteries can make all the difference in a poorly behaving central furnace system.