Your furnace is supposed to give hot air to warm the household. When it’s blowing cold air instead of hot air, it’s evident that something’s wrong with it, and you need to take action.
Some of the problems aren’t major, and you can try to fix them on your own. However, significant issues can make the furnace blow cold air instead of hot air, in which case only the professionals will help.
Here are some of the most common problems making your furnace not blowing hot air, so keep reading for the details.
Page Table of Contents
- 1. Thermostat-related problems
- 2. The oil tank is empty
- 3. Issues with the computerized features
- 4. The furnace is overheated
- 5. The pilot light is damaged.
- 6. Faulty thermocouple
- 7. Faulty electronic ignition
- 8. Valve issues
- 9. Faulty flame sensor
- 10. Blocked oil filter
- 11. Dirty oil or gas burner
- 12. Ducts are leaking
In a big household, people could have different opinions about what hot air means for them. Someone could set the thermostat fan setting from Auto to On, so the fan will run without stopping or generating heat. You will have to switch it back to Auto so that your furnace blows hot air again. It’s an easy fix.
If you’ve recently installed the thermostat, maybe you’ve missed some steps of proper installation. Also, the thermostat may not match your furnace, rending it to blow cold air. It’s better that you call the HVAC technician for a checkup.
If the thermostat runs on batteries, they could be dead, so the thermostat cannot run and send the request for hot air. Replace old batteries with new ones and see if that fixes the problem.
2. The oil tank is empty
Should you have an oil-fired furnace, it could be out of fuel. If that’s the problem, the blower will still circulate cold air even if the burners cannot light and generate heat.
3. Issues with the computerized features
Modern furnaces are great as they come with numerous features for best accuracy and control, but the electronic components also pose a high risk for malfunctions. If the furnace comes with an electronic control panel, you may have to reset the system. Attempt to turn off the furnace via the power switch. Restart the furnace after a couple of minutes. It’s similar to you rebooting the computer in case of a software glitch.
If restarting the furnace doesn’t solve the problem, something else could be wrong, and you should call the professionals.
4. The furnace is overheated
When was the last time that you’ve checked the filter? A clogged air filter doesn’t allow air circulate, so the furnace works harder and eventually overheats. Most furnaces today come with safety features and turn off automatically in case of overheating. Therefore, your furnace doesn’t blow hot air anymore.
You should check the air filter and replace it with a new one, mostly if you haven’t returned it for a long time.
5. The pilot light is damaged.
Old furnaces feature a continuous pilot light that can cause problems if it’s out. A gust of air from someone working close to the furnace can turn off the pilot light. It’s possible to relight the pilot light on your own, but don’t hesitate to call the professional if you’re not comfortable doing it.
6. Faulty thermocouple
If you can relight the pilot, but it still goes out, a faulty thermocouple may cause the furnace to generate cold air. The thermocouple is a sensor that monitors the ignition and the gas valve. It’s not very complicated to address a faulty thermocouple, but only a technician should make the adjustment or the replacement, if necessary.
7. Faulty electronic ignition
For customers with new furnaces with electronic ignition, such as hot surface ignition or intermittent pilot, adjustments or replacement of faulty components may be necessary. Unless you’re a certified HVAC technician with electronics experience, you shouldn’t try to fit it on your own.
8. Valve issues
When the pilot doesn’t light at all, a faulty gas valve makes the culprit. If the system wasn’t cleaned for some time, debris or dirt could block the valve and affect the functioning. Either way, it’s best to call a professional for cleaning and checking of the furnace.
9. Faulty flame sensor
When the furnace begins to blow warm air, but it suddenly turns to cold air, you need to look at the flame sensor. When the flame sensor is worn out, or it’s covered with grime, the burner will keep on turning off, so the air blown in the house is cold.
It’s advised to call the HVAC technician for furnace repair as it’s tricky to address a flame sensor.
10. Blocked oil filter
In oil-fired furnaces, dirt and debris may collect and cause the filter to get clogged. A clogged filter will affect ignition, and the furnace won’t blow hot air anymore.
It’s possible to clean and replace the filter on your own, but you should leave it to the pros if the mess is too much, and the replacement isn’t as straightforward as expected.
11. Dirty oil or gas burner
When it comes to furnaces, regular maintenance is essential for proper functioning. It would help if you didn’t skip the furnace burner, as collected grime and dust may affect good ignition. It’s best to call a professional for cleaning the burner from time to time.
12. Ducts are leaking
If your furnace is blowing cold and not hot air, the hot air could escape through some holes in the ductwork carrying the heat throughout your house. It’s always a good idea to check the ducts and the furnace when your home is getting colder instead of warmer.