Check Furnace Thermostat Settings Incorrect thermostat settings can be the cause behind no heat coming out of the vents, even with the furnace blower turned on. Check the thermostat to ensure the setting is in HEAT instead of COOL. It is a common mistake that happens. The fan runs continuously when it is switched on.
Clogged or Dirty Air Filters
A dirty or clogged air filter can restrict airflow, causing your furnace to overheat and shut off the burners. In such cases, the blower fan will continue running, but no warm air will be distributed throughout your home.
You may have a faulty sensor, sticky motor, bad controller board, too many closed dampers, a blocked air return, incomplete combustion, cracked heat exchanger, blocked condensate line, etc etc. some of these things are life-critical situations. The blickenlights will tell you.
If your HVAC system isn't blowing warm air, start by checking the thermostat settings and batteries; more complex issues like faulty wiring or ignition system problems may necessitate professional assistance. Airflow restriction due to clogged air filters can result in your system blowing cold air.
While furnaces can stop operating for complicated reasons, home owners should check a few usual suspects first behind a lack of hot blowing air: Electrical problems causing a loss of power. Blocked air vents and ducts restricting airflow. Improperly configured thermostat settings.
Check your thermostat's batteries and replace any that are exhausted or defective. Clean all of the parts of your furnace, especially the ones that are susceptible to dust and dirt. You could also hire HVAC technicians to clean the system thoroughly. Ensure that the gas valve is open and not obstructed by any debris.
The most common reason a heat pump is blowing cold air through your air vents is defrost mode. This is a safety feature to melt frost and ice within the system. During defrost mode your heat pump made switch modes to heat up the outdoor coils. Indoor temperatures will fall because the system is briefly in cooling mode.
It's most likely an incorrect thermostat setting if you find your furnace blowing warm air, not hot. The fan is set to “on” instead of “auto.” Furnaces only pump hot air until the thermostat setting is reached, so if your fan is always on, it will blow both hot air when the furnace is heating and cold when it's not.
If the filter is clogged, replace or clean it immediately, then rerun the furnace. If this does not correct the airflow issue, make the call for help, as it's likely an issue with an internal component, such as the blower or control board, that will require an experienced technician to diagnose and repair.
If your furnace is blowing hot but your home is still cold, it may be a problem with your ductwork. You may have leaky or damaged ducts that are letting hot air escape and cold air in. Sometimes a damper in the system can get miss-adjusted or come loose, thereby inadvertently blocking or reducing airflow.
Short cycling is a common sign of a bad flame sensor. The sensor thinks that there isn't a flame, so it shuts off the gas as a safety mechanism. Except, there is a flame and without the gas to supply it, it dies. This is a frustrating problem, but an HVAC technician can fix it.
If your furnace won't turn on but fan works, it could be that the pilot light (or ignition switch) is out. A nifty safety feature that your furnace has that you may be unaware of is your pilot light which prevents pumping natural gas or propane into your home.
If the fan limit switch malfunctions, the blower might continue to operate even when the furnace is not heating the air, resulting in your furnace blowing cold air from your registers. Or, it may prevent the furnace from operating at all. Check your air filter, and clean or replace it if needed.
The thermostat is the command center for your heating system, and when it malfunctions, it can lead to your furnace blowing cold air. Incorrect thermostat settings can be a simple oversight, but it can also result from battery problems in non-hardwired systems or from outdated technology in older thermostats.
Check Furnace Thermostat Settings
Incorrect thermostat settings can be the cause behind no heat coming out of the vents, even with the furnace blower turned on. Check the thermostat to ensure the setting is in HEAT instead of COOL. It is a common mistake that happens. The fan runs continuously when it is switched on.
In most newer systems, the button is often directly next to the blower motor, while in older systems, it may be harder to spot as it is sometimes underneath or behind the motor. The reset button is often made of yellow or red plastic and marked with a large “R ” to make it easier to spot.
There are several reasons why your furnace may not turn on. The most common include a broken thermostat, gas line issues, clogged air filters, blocked ductwork, a tripped circuit breaker, and issues with the furnace itself.
Typically, there's a 10 to 15 minutes allowance for this. However, if after this time it's still producing cold air, then there's an underlying problem that needs to be addressed. It would be wise to turn the furnace off and get in touch with a pro immediately for help dealing with the issue.
Check Your Furnace Air Filter
Next, check your heater's air filter, as this can cause a furnace to stop blowing air. Your filter could be so saturated with dust and debris. In that case, even though the furnace is actually blowing air, your clogged filter is blocking it from making it into your ducts.
If your furnace is not blowing hot air, or is not operating at all, a component called the fan limit switch or high limit switch may have malfunctioned. You may also see an error message on your thermostat, or a blinking LED light on the furnace control board.
Leaky Air Ducts
Your heater might also be blowing cold air because of leaky ducts. Leaks in your ductwork can cause warm air to escape before it reaches your rooms, causing cool air to come through the vents. A leak can occur because of poor insulation, aging ducts, or damage.
This could be simply because the vent air's temperature is below your body temperature. Check this by looking at your thermostat and observing the inside temperature.