What Safety Features Are Found in Modern Furnaces?
A gas furnace heats your Atlanta home using a combustible gas and controlled fire. Modern furnaces have safety features, including a flame rollout switch, a high-temperature limit switch and furnace flame sensors to help keep your home safe.
What Is a Flame Rollout Switch?
As your furnace starts its heat cycle, the air is pulled through the furnace and out of the flute using the draft inducer fan. This produces the humming sound you hear when you first turn on your thermostat or when your thermostat calls on your furnace for more heat.
The draft inducer fan will run for between 15 and 45 seconds based on the furnace model, and then the gas burner will ignite, making the whooshing sound you hear. The draft pulls the flames into the heat exchanger.
About 60 seconds later, the primary blower activates and starts drawing air from your house via the cold air returns. The cold air travels over the heat exchanger, and heat is transferred into the cold air. The newly heated air is pushed through the supply register vents to the different rooms in your home.
A flame rollout is when the burner flame rolls out of your furnace’s heat exchanger. Instead of just heating the heat exchanger, stray flames are heating parts of your furnace with important control components.
If this situation is not rectified quickly, internal components of your furnace, like its control board and wiring, might be destroyed. This could lead to a serious fire hazard.
The flame rollout switch detects the presence of a flame rollout and turns off the gas valve. Of course, as a result, your furnace will no longer fire. Its draft inducer fan might keep running, and the primary blower will run until all of the heat built up in the furnace has been distributed.
However, the furnace will no longer produce flames, eliminating the potential danger and damage. It will go through its normal cooldown process but will not start up again until the flame rollout switch has been reset.
If you believe your flame rollout switch is defective, do not try to bypass it. It performs a vital safety function, keeping your home safe and your furnace in good condition. Instead, we recommend that you contact the professionals at Bardi Heating, Cooling & Plumbing. Let us evaluate the issue with your rollout switch and suggest replacements or repairs.
Where Is the Furnace Flame Sensor?
The furnace flame sensor sits on the opposite side of the igniter. For example, if the igniter is on the left side of the burners, you will find the flame sensor on the right side of the burners.
The flame sensor is designed to prevent unburned gas from seeping into your home. It detects whether your furnace is burning the gas it’s receiving and producing a flame.
When you look inside your furnace, you will see a small rod in front of the burners. If your burners are producing a flame, that sensor detects the flame and tells your furnace control that everything is okay and it can continue to receive natural gas and burn it.
However, if the control board does not get a signal from the flame sensor within a couple of seconds of the gas valve opening, the control board identifies a problem. It will shut down the furnace, stopping unburned gas from leaking into your home.
A dirty flame sensor can cause problems in your furnace. Since it does not detect a flame, even if one is present, it will constantly tell your furnace to shut down. A good way to prevent this annoying problem from happening and to determine if your flame sensor is functioning properly is to contact our professionals at Bardi Heating, Cooling & Plumbing. We can clean your furnace and flame sensor during our annual maintenance service.
High-Temperature Limit Switch
Your furnace’s high-temperature limit switch is a small yet critical device. It’s also referred to as the limit switch or the fan limit switch. Its two key functions are turning the fan on and off during the furnace’s heating cycle and shutting down the furnace if its interior temperature gets too high.
The limit switch has a long temperature sensor with a probe connected to a mounting plate. The mounting plate has multiple terminals connecting to control wires for the blower fan and the gas valve. Many modern furnaces have multiple limit switches that check the temperature in different parts of the furnace.
When your thermostat indicates the need for heat, the burners ignite and start to heat the heat exchanger. For the first few minutes, the air in the heat exchanger is not hot enough to warm your house. So your limit switch stops the blower from turning on. The limit switch activates the blower fan and circulates heated air through your house when the air reaches the desired temperature.
Once your house reaches the set temperature on the thermostat, the burner deactivates. However, the limit switch keeps the blower running to extract the maximum amount of heat from the heat exchanger. Once the air in the heat exchanger drops to a lower setting, the switch turns off the fan until the heating cycle begins again.
If the heat exchanger gets too hot throughout this process, it can crack. This ruins your furnace. The heat exchanger can overheat if there’s an issue with your blower fan, if there is a dirty filter, or if there is some other malfunction that’s restricting airflow through the furnace exchanger. In these cases, the limit switch shuts off the burner to prevent damage.
You will know that this key safety feature of your furnace is malfunctioning if the blower fan does not shut off. Additionally, a bad switch can stop the furnace from operating if it fails when it is stuck with an open circuit or in the off position.
In modern furnaces, if a limit switch is triggered four or five times and has to shut off the burner, the computer control of the furnace can go into a hard shutdown mode. This will prevent the furnace from turning on until it has been serviced by professional HVAC technicians.
Fan Limit Sensor
The blower pushes cool air over the heat exchanger and distributes the heated air through your home. If the blower is not working properly or not providing enough airflow over the heat exchanger, the fan limit sensor turns off your furnace.
If the fan limit sensor isn’t working right and malfunctions, your heat exchanger will get hot but won’t have the air from the fan to draw the heat away. This will lead to cracks and splits in the steel, which are dangerous and allow carbon monoxide into your home.
Trusted Home Experts in Atlanta
At Bardi Heating, Cooling & Plumbing, we are proud to be Atlanta’s top HVAC and plumbing company. We are family-owned and have been serving the Atlanta area since the late 80s. We are home to NATE-certified technicians, pride ourselves on honesty, and are proud of our A+ Better Business Bureau accreditation.
Our services include HVAC installation, replacement, maintenance, and tune-ups. We offer duct cleaning, plumbing services, water heater repair services, tankless water heater repair, indoor air quality testing, and gas pipe repairs. Contact Bardi Heating, Cooling & Plumbing today. Let our skilled technicians and plumbers assist you with any project, no matter how big or small.
