Why Won’t My Furnace Turn On When the Temperature Drops?

Even though Georgia doesn’t get as cold as many more northern locations, it can still be frustrating to find that your furnace won’t turn on when you need it. Unfortunately, this issue can occur for a variety of different reasons so it is not always easy for you to diagnose why your furnace isn’t working. With that in mind, here are the most common reasons why a furnace won’t turn on and what can be done about them.

Electrical Supply Issues

If you have an electric furnace, it obviously won’t work if it isn’t receiving electricity for any reason. What some people don’t realize is that gas furnaces also won’t be able to turn on without electricity. A gas furnace requires electricity first to turn on its inducer fan and then for the electronic igniter that works to light the unit.

If your furnace circuit breaker is tripped or there are any electrical issues with the furnace itself or the wiring that runs to it, your heating won’t ever turn on. A tripped circuit breaker is a fairly common issue that can sometimes result from the furnace overheating or having an issue that overloads the circuit, and this is always the first thing you will want to check if your furnace won’t turn on.

Interrupted Gas Supply

Gas furnaces obviously won’t be able to light if gas isn’t flowing to the unit for any reason. If you have a gas stove, water heater or any other gas-burning appliances, you will want to check to see if they still have gas flowing. If none of your gas appliances are working, you will need to contact your gas supplier to see what the issue is. If gas is only not flowing to your furnace, you should check that the gas valve is fully open.

One possible cause of this issue is that the gas valve in the furnace is broken and stuck closed. The furnace’s pressure switch signals the gas valve to open when the furnace needs to light, while the flame sensor works to close the valve if the furnace doesn’t light immediately. If the valve breaks, no gas will flow and the furnace won’t light.

Faulty Electronic Igniter

Most all modern furnaces use some form of electronic igniter instead of the traditional standing pilot light found on older units. Electronic igniters are great because they eliminate the energy waste that comes from using a standing pilot light, and they are also far more convenient since you never need to worry about a pilot light going out. Like any other furnace component, the electronic igniter can sometimes malfunction or fail entirely. Should this happen, there will be no way to light the gas and the furnace won’t turn on.

Pilot Light Is Out

If your furnace was installed before 2010, there is a decent chance that it does use a standing pilot light. If so, the very first thing you should do if your furnace won’t turn on is check that the pilot light is still lit. Pilot lights can easily get blown out by a strong gust, and the pilot will also obviously go out if the gas supply is ever interrupted.

Pilot lights can also go out or fail to relight due to various issues. Most commonly this happens because the thermocouple that detects if the pilot is light is dirty, bent or worn out. It could also be that the pilot gas tube is clogged or the pilot control is faulty and needs to be replaced.

Dirty or Faulty Flame Sensor

A dirty or broken flame sensor won’t prevent your furnace from turning on. However, it will cause your furnace to shut off within a few seconds automatically. The flamer sensor is an important safety feature found on all furnaces that use an electronic igniter.

As the name suggests, it detects whether the furnace’s burners are lit to ensure that gas won’t continue to flow if the burners fail to light. If the sensor doesn’t detect the heat from the flames within a few seconds, it will instantly signal the gas valve to close.

The flame sensor can sometimes wear out due to age and need to be replaced. However, the more common issue is that the sensor is covered in dirt and grime, which insulates it and prevents it from detecting the heat from the flames. This is one of the easiest problems to avoid as it all takes is having your furnace professionally maintained every year as one part of this is cleaning and testing the flame sensor.

Worn-Out Inducer Fan Motor

The very first thing that happens when your furnace goes to turn on is that it switches on the inducer fan. The inducer fan draws any remaining combustion fumes out of the combustion chamber and heat exchanger. This is important as these fumes are inflammable and can prevent the gas from igniting. When the inducer draws air up through the furnace, it creates suction that activates the unit’s pressure switch. The pressure switch is then what signals the gas valve to open and the electronic igniter to activate and light the furnace.

The inducer fan motor can wear out, and this will prevent the pressure switch from activating and the furnace from turning on. The only solution to this issue is to have the motor replaced.

Malfunctioning or Broken Pressure Switch

The pressure switch itself can also malfunction or break and get stuck in the closed position. Again, if the pressure switch doesn’t activate, the gas valve won’t open and the furnace won’t light. In some cases, the issue is fairly easy to fix by repairing or replacing the switch’s suction tube, but there are also times when the entire pressure switch will need to be replaced.

Malfunctioning or Improperly Calibrated Thermostat

There are also many cases when your furnace fails to turn on due to issues with your thermostat. It could simply be that you don’t have the thermostat set correctly or turned to heat, and there is always a chance that your thermostat is faulty and needs to be replaced. You should also check that the display isn’t showing a low battery alert as this means that the batteries no longer have sufficient charge to signal the heating system to turn on.

Thermostat location is also much more important than most people realized. If your thermostat is in a location that stays warmer than the rest of your home or in a place where it is exposed to direct sunlight, it can interfere with its ability to measure your home’s temperature properly. In this case, the thermostat may not signal the furnace to run even when most of your home feels freezing cold.

If your furnace won’t turn on or is experiencing any other issues, the expert technicians at Hitchcock Heating & Air are ready to help. We service and repair all makes, models, and types of furnaces, and we also specialize in furnace replacements and installation. We also offer a full range of cooling and indoor air quality services, and we serve both residential and commercial customers in Rome and the surrounding areas.

Give us a call today to schedule a furnace inspection or any HVAC service.

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