SERVING 
Here in Atlanta, our winters are pretty mild. But it sure doesn’t feel that way when your furnace quits!
Every winter, we receive calls from folks who ask, “Why is my furnace not heating?” The truth is, there are lots of reasons a furnace could stop sending heat into your home. Some problems are easy to fix, but others are more complex! To get to the bottom of it, we usually have to visit your home and examine your heating system.
With that in mind, here are some of the most common reasons your furnace won’t heat up when you need it to.
When you notice the gas furnace not heating…
The first thing to remember is not to panic! You might be able to get it going again without calling an HVAC technician for service. Before calling for assistance, we recommend that you:
- Check the temperature setting on your thermostat. It’s possible that someone changed it and didn’t tell you! Just set it back to the target temperature and wait for the heat to come on.
- Replace your air filter. If the furnace is starved for return air, it won’t heat properly. Most disposable air filters are designed to last for 90 days. Replace yours if it’s been there longer than that.
- Check the breaker box. If the breaker for the furnace is tripped, the furnace won’t turn on. Flip the switch and try again. If the breaker keeps tripping, you might need to call an electrician.
- Reset the disconnect switch. Occasionally, this switch gets bumped when someone is doing maintenance. Check it to make sure it’s in the “on” position.
- Open all your air vents. When registers are closed or blocked, the system won’t adequately heat your home.
- Open the gas valve. If you closed it and forgot about it, you’ll need to open it again to get gas flowing to the furnace.
- Light your pilot light. For older furnaces, you will need to manually light the pilot light if it goes out.
If your furnace stops heating due to one of the above problems, you’re in good shape! These are easy things for homeowners to address on their own.
But if you’re still not sure what’s going on with your furnace, don’t worry. There’s a good chance that whatever is wrong is easy for a technician to fix.
Possible Reason #1: The inducer fan motor pressure switch
This is a simple fix for an HVAC technician… if you know what to look for!
Most furnaces contain a pressure switch that activates when the vent pipe is blocked or clogged. This is actually a safety feature because it stops your furnace from running (and producing exhaust gasses) if those gasses can’t vent.
So if the furnace isn’t running, there could be a blockage in the vent pipe. But in other cases, the switch itself gets clogged with dirt or other debris. This will have the same effect as if the vent pipe was blocked: the fan motor won’t turn on.
The solution is to remove the inducer fan motor and clean it. After that, the switch usually starts working properly again.
Possible Reason #2: Failed hot surface igniter
Unless you have a really old furnace, you probably don’t have a pilot light. Instead, you’ve got a hot surface igniter that saves you from having to manually start a flame to run your furnace.
This particular component tends to fail sooner than lots of other furnace parts. In fact, hot surface igniter failure is so common that we always check this component during our annual furnace maintenance visit for PV Priority Plan customers. If you’ve got a furnace that’s not heating, there’s a good chance you have this problem.
Most contractors stock hot surface igniters and can replace yours during the initial visit.
Possible Reason #3: Your air filter is filthy
We already mentioned this one above, but it’s a super common problem that bears repeating.
For a furnace to heat air properly, it needs air moving through it. A good air filter will allow a sufficient volume of air to enter the unit while trapping or blocking dust, debris, hair, and other small bits that can otherwise collect inside the furnace.
After a while – typically three months for disposable filters – the filter needs to be replaced or cleaned. If the filter gets super dirty, it will reduce airflow and lead to reduced furnace performance.
Basically, the furnace will still run, but it won’t work very well.
It will also cost a whole lot more to operate while not really providing enough heat to keep you comfortable. The solution is to replace or clean the filter, depending on what kind it is.
Possible Reason #4: Lack of maintenance
Furnaces are like cars. They need regular maintenance in order to run properly.
If you forget to have your furnace serviced before winter rolls around (and don’t beat yourself up about it – it’s easy to forget!), a lot of things can go wrong:
- A dirty flame sensor will prevent the system from lighting the furnace burners.
- The blower motor can get too dirty, which prevents the heat exchanger from working properly.
- Dirty burners will reduce system performance somewhat and make your furnace work harder than it needs to.
Annual maintenance can prevent these problems before they happen at all! PV Priority Customers get two visits per year, so you know your HVAC system is prepared for every season.
Possible Reason #5: Too much gas
Another possible reason your furnace isn’t heating is that it’s getting too much gas.
Furnaces that aren’t properly calibrated can result in overheating. This will make the furnace cycle on a limit switch, and it won’t be able to keep up on really cold days. If you’re having this problem, an HVAC technician can reset the amount of gas getting to the furnace so that it aligns with manufacturer specifications.
Possible Reason #6: Failed draft inducer
This little motor, also known as the inducer draft motor, helps remove gas from the heat exchanger. Over time, this component can fail and burn out. It can also get dirty (regular maintenance prevents this) and cause the furnace’s safety switches to activate.
Whatever the case, you will need to replace it. Be sure the HVAC technician replacing your draft inducer takes flue gas samples to test the overall functioning of your burners and heat exchanger.
Possible Reason #7: Ductwork problems
We see ductwork issues in most of the homes we service! Some aren’t super serious, but others are downright egregious. Examples include:
- Ducts that are the wrong size
- Bent or kinked flex duct
- Poorly installed ducts
- Unsealed, leaky ducts
- Ducts damaged by animals
Bad ductwork can’t move all of the hot air your furnace is producing. You might have the best furnace in the world, but it won’t matter if your ducts are damaged or improperly installed!
Getting ductwork right isn’t a guessing game. It’s a science. The right solution is to perform standard calculations that determine the right size, type and routing for your home’s air ducts. After that, they need to be installed in a way that will minimize the risk of damage.
Furnace not heating and you aren’t sure what to do?
We’ve got you! PV provides comprehensive furnace repair services to homeowners throughout the Atlanta Metro region.
If you’re struggling with a furnace that won’t heat properly (or at all), simply give us a call at (404) 282-2909 today! You can also schedule service using the form below.
