Gas furnaces are extremely complex and can experience a wide variety of issues that prevent them from working properly. A furnace that runs for hours at a time is a problem since it leads to increased wear and tear and higher heating costs. However, this isn’t necessarily an emergency as long as the furnace still keeps your home from getting too cold. On the other hand, there are many issues that are definitely considered an emergency and are something you’ll want to have fixed right away.

What Is Considered a Furnace Emergency?

In truth, most furnace problems are considered an emergency since they will typically lead to the furnace not running or shutting down almost immediately after igniting. If your furnace doesn’t work, the temperature in your home will quickly start to drop and could become cold enough that your pipes freeze and possibly burst.

A furnace that suddenly starts giving off a strong burning smell is also an emergency. A burning smell is normal when you turn on your furnace for the first time in the fall, but the smell should go away fairly quickly. If you notice a burning odor any other time, you should immediately shut off the furnace to prevent it from being damaged and reduce the risk of a fire. An acrid burning smell coming out of your vents often indicates that the wiring in the furnace has started to melt or that the flames are escaping the combustion chamber.

Electrical Issues

Many of the components in a gas furnace require electricity to run as they send signals to and receive signals from the control board. The thermostat also sends a signal to the control board when the furnace needs to turn on and off.

The process that happens once the thermostat calls for heat and signals the furnace to run is much more complicated than many people realize. Once the control board receives the signal from the thermostat, it first signals the draft inducer to run. The inducer works to draw latent fumes out of the combustion chamber to ensure the burners ignite properly, and it usually runs for around 30 seconds before the furnace ignites.

The inducer creates positive air pressure, which triggers the pressure switch to close. When the switch closes, it completes a circuit and sends a signal to the control board for the gas valve to open. At the same time as the gas valve opens, the electronic igniter also comes on to light the burners. The flame sensor then has to detect that the burners are lit or else it will signal the control board to close the gas valve. Once the burners are lit, the low-temperature limit switch then monitors the temperature of the heat exchanger. Once the exchanger reaches a certain temperature, the limit switch then signals the control board to turn on the blower so that air starts being drawn into the furnace.

The control board might fail or an electrical issue such as a loose connection or damaged wire could prevent it from sending or receiving the signals from the various components. If so, the furnace typically won’t run or will shut off within a few seconds of it trying to start. Electrical issues may also lead to the furnace turning off midway through a heating cycle.

If a furnace has any electrical issues, the wires can also short circuit and cause the circuit breaker to trip. As such, it’s always a good idea to check if the circuit breaker is tripped any time your furnace doesn’t turn on when it should.

Failed Electronic Igniter

The electronic igniter is often one of the first components that will fail in your furnace. Many modern furnaces use a hot surface igniter to light the gas burners, which is somewhat similar to a lightbulb filament. When the furnace starts, the control board closes a circuit so that electricity flows through the igniter, causing it to become red hot. All of the heat radiating off the igniter then lights the gas that flows out of the burners.

A hot surface igniter experiences massive temperature fluctuations since it gets extremely hot when the furnace starts and then quickly cools down once the furnace shuts off. These temperature fluctuations can cause the igniter to break or crack so that it no longer works, which will obviously prevent the furnace from igniting. Hot surface igniters will sometimes only last for five years or so before needing to be replaced. This is one of the first things a technician will check if your furnace won’t run.

Dirty or Worn-Out Flame Sensor

Flame sensor issues are one of the easiest problems to diagnose. A dirty or worn-out flame sensor won’t prevent your furnace from igniting. It will typically lead to the burners only staying lit for a few seconds before the gas valve again closes and the flames go out. In many cases, flame sensor issues will lead to the burners continually lighting and shutting off over and over again in quick succession.

The flame sensor works by continually sensing the heat coming off the burners to ensure they stay lit. As the sensor starts to wear out, it may also malfunction and occasionally stop working. If that happens, the furnace shuts off before it completes a full heating cycle.

When the burners are lit, a small electrical current flows between the ions in the flames and the flame sensor conducting rod. The control board constantly monitors this current to ensure gas doesn’t continue to flow if the burners aren’t lit. If the sensor breaks, doesn’t directly contact the flames or is too dirty, the current won’t flow and the control board will close the gas valve. In some cases, flame sensor issues can lead to the furnace suddenly shutting down in the middle of a heating cycle.

Worn-Out Blower Motor

A worn-out blower motor is also an easy problem to diagnose. You’ll still hear the furnace ignite, but the blower won’t ever run, and no air will flow out of the vents. The blower could fail and not start or malfunction and not bring sufficient cool air into the furnace. If so, the furnace will only run for a few minutes before it begins to overheat. When this happens, the high-temperature limit switch will trigger and the control board will automatically shut down the furnace.

Draft Inducer Issues

A failed draft inducer motor will lead to nothing happening when the thermostat calls for heat. This is because the inducer is the first thing that comes on when a heating cycle starts. If the motor fails or the inducer doesn’t work properly, the pressure switch won’t activate and signal the gas valve to open. The pressure switch itself can also break, in which case you’ll hear the inducer running, but the gas valve won’t open and the furnace won’t ignite.

Clogged Exhaust Flue

The draft inducer draws the combustion fumes through the furnace’s heat exchanger and then into the exhaust flue so that the fumes are safely vented outside. If the flue is clogged or has any issues that prevent the fumes from being vented outside, it can create negative pressure inside the furnace. Negative pressure causes the pressure switch to open, which will lead to the control board closing the gas valve and the furnace shutting down. A flue that is clogged or not venting properly is one of the most serious issues. This is because it can allow carbon monoxide to escape and leak out into the ductwork or the surrounding area.

Universal Heating & Cooling is the top choice for all of your emergency heating and air conditioning needs in Dayton. We are available 24/7, and our technicians can quickly diagnose any furnace, heat pump or AC issues and get your heating or cooling system working again. We also offer professional HVAC installation, replacement and maintenance services, so give us a call for all of your home’s heating and cooling needs.

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