How to Fix Furnace that Won’t Turn On

It’s winter again, the winds are blowing in, we can see snippets of snow, and of all the times your furnace had to be faulty, it had to be now. It is literally the worst timing for this to happen ever, but before you run over to an electrician, you need to find out why it’s not working. 

You may find that it’s something you can fix all by yourself, and you don’t need to spend all that money on paying someone to repair it for you. In this article, we will share with you the 10 common, possible causes and fixes of a faulty furnace.

Furnace Won’t Turn On? Possible Causes and Fixes

1. Malfunctioning Thermostat

There are a lot of things that could go wrong with the thermostat, some more technical than the others. For instance, when the furnace is blowing out cold air instead of hot, often, the furnace is not the problem. It is the thermostat.

Here are some ways you can fix it:

  • Set the thermostat to “auto.” Suppose the thermostat is permanently set to “on,” then the furnace will blow out cold air eventually. Leaving it at “auto” will allow it to work appropriately and blow only hot air. 
  • Charge the thermostat’s battery. If your furnace runs on batteries, you should be charging them at least twice a year. If the battery is low, it will affect the furnace’s effectiveness. 
  • There was a mistake during the installation. This usually happens when people try to fix it themselves. While it’s an admirable thing to do, it is still better to hire a professional to fix it for you.
  • Check the thermostat for dirt. It is very easy for dust, dirt, and other stuff to accumulate and clog up a thermostat, so check regularly and dust it off. 
  • Turn off the breaker and check the fuse needed to get the furnace. 

2. Your Furnace Might Be Old

Furnaces usually last for a really long time. They last as long as 20 – 30 years when maintained properly, but you can’t ignore the role of the manufacturing company. The materials used in making the furnaces matter a lot. 

If you bought it from a company that uses substandard materials, your furnace has a lesser chance of lasting for 20 years. Heck, it might not even last for 10 years. If this is the situation, there are only two things you can do:

  • Check the warranty of the furnace. If it’s still within its warranty period, take it back to the company and request for it to be exchanged for a new one. 
  • If it’s past its warranty period, you will need to buy another one. From a different company if possible. 

3. Faulty Gas Line

The gas line supplies fuel to the whole house, so if your furnace isn’t working well, you may have to check to see if it’s a general problem or not. Here are a few ways you can fix it:

  • If you find that the gas line is set to “off” or “close”, change it to “on” or “open”. This is if it is a general gas supply problem. 
  • If every other gas-fueled appliance is working, check the gas line that is directly linked to the furnace. The pipe is traceable from the furnace itself. Adjust it until your furnace starts working again.
  • Check the gas valve. Just like the thermostat, dust and debris can get clogged up inside the gas valve and cause it to stop working altogether. Or the valve could simply be old. These things wear out eventually. If this is the case, you should consider getting your valve cleaned regularly. It will help you maintain it for longer. 
  • Confirm that there’s no leakage. The moment you begin to perceive the smell of gas, call a professional for help and leave the house immediately. 

4. Clogged Air Filters

Furnaces have filters that allow the easy movement and flow of air through them. They play a vital role in how well the furnaces work, so a faulty furnace could mean a faulty filter. The good thing is, this problem can easily be fixed:

  • Air filters can’t really be “cleaned”, so when one is clogged up and to avoid it getting clogged up at all, change them regularly. It should be a part of your furnace maintenance routine. Some furnaces are designed to naturally shut off when the filters get clogged. 
  • If the problem persists after changing it, hire a professional to clean the air ducts. 

5. Problems With The Pilot Light

One way to detect when the pilot light is the issue is when the furnace won’t ignite. It is the number one cause of that problem. All gas-fueled furnaces have them. It acts as a sort of ignition sensor. There are a few ways to fix them:

  • If the sensor is dirty, remove and clean thoroughly. Make sure you turn off the gas line that links directly to the furnace before starting.
  • If the pilot light merely went off, check the instructions on the body of the furnace for how to relight it. 

If, after everything, nothing works, call a professional. 

6. Bad Limit Switch 

A limit switch is a device that reads the temperature of the plenum and waits for it to get to the right degree of warmness. When overheating occurs repeatedly, it goes bad and shortens the lifespan of the blower and furnace as a whole. It is also not easy to locate. 

We wouldn’t recommend fixing this yourself; it will be much better to call a professional to work on it. That is if it is the reason why the furnace isn’t working. 

7. Dirt Gas Valve

Another reason why your furnace might not be working is your gas valve. Like every other part or component of the furnace, the gas valve also needs to be maintained. If you check and confirm that the gas valve is indeed the problem, here are some things you can do to fix it:

  • Clean the gas valve. By now, you must have noticed already that dirt accumulates easily in furnaces, and the gas valve is not excluded. Clean off every dirt, dust, and debris on it to unclog it and see if the furnace starts working.
  • Sometimes, it might not be dirty, just worn out. In this case, you will need to change it. 

8. Worn Out Air Ducts

Along with the filters, the air ducts are primarily responsible for getting air through the furnace and into your house. Being placed outside the heating area means they are subject to extreme temperature changes, which can easily cause them to weaken and start leaking. 

Leaking can also occur when the ducts are not fixed properly, or they come unhooked. When this happens, the cold air surrounding it will come in, and the warm/hot air will go out. If this happens:

  • Use duct tape to seal the leak spot. Locate the exact spot or spots where it is leaking from. If it’s a small one, duct tape will be enough to seal it. 
  • Change the ducts. If the leaks are bigger and more severe, mere duct tape won’t cut it. You will need to have it changed completely.
  • If the ducts come unhooked or are not appropriately fixed, simply fix them correctly by yourself or securely hook them back together. 

9. Cluttered Furnace Area

Avoid pilling up furniture, appliances, and other possessions in your furnace area. Tight spaces may cause the furnace not to function as efficiently as it should. Also, avoid putting flammable or combustible materials close to it to avoid fire mishaps. 

You need to give your furnace room to “breathe” and clean it regularly as well. If the outside area is clean and free of dust, dust will be less likely to get into the ducts, gas valves, filters, etc. 

10. The Furnace Itself

Sometimes, the furnace itself is the problem. The home circuit breaker could be the one with the fault, and when it is faulty, it stops heat from being produced. Or the furnace switch inside has been tripped off. When any of this happens, try these solutions:

  • If it is the circuit breaker, test it and flip it on. make sure it stays there,
  • If it’s the switch, check that the power hasn’t been disconnected from it and switch it on too.

If both of them keep tripping, then there is a fault with the whole wiring, and you should get an HVAC professional to fix it for you. 

General Tip On How To Make Your Furnace Last Longer

As you have seen, one underlying common factor to each of these problems is dirt. As long as you keep your furnace and the area it is kept clean, it will last as long as it is expected.

Make sure you change whatever needs to be changed regularly, clean out dirt and dust as often as possible too. It will go a long way, but if you would like to change a new heating device, read our guide on fireplace inserts to get started.