Gas-powered furnaces are complex appliances with many parts. Every component must do its job well for the heating system to generate and distribute heat, including the pressure switch. But exactly what does a pressure switch do on a furnace?
Many homeowners count on Green Energy Mechanical Inc. for professional furnace repair in Canton, Massachusetts. Our family-owned company with NATE-certified technicians can service all furnace makes and models. Here’s what our heating experts have to say about pressure switches and their functions.
What a Furnace Pressure Switch Is and How It Works
A pressure switch is a safety mechanism on gas furnaces that ensures the heating unit doesn’t retain exhaust fumes. When your thermostat triggers the furnace to kick on, the inducer motor is the first component that turns on. This motor creates negative air pressure inside the equipment to force any remaining exhaust fumes in the heat exchanger out through the flu pipe.
If your gas furnace runs while its heat exchanger contains traces of hazardous gas byproducts from its previous cycle, it could hold too much gas, resulting in a backdraft that disperses gases from the heating system into the house.
What does a pressure switch do on a furnace? The switch detects the negative air pressure using an elastomeric diaphragm. When the furnace and inducer motor turn on, the diaphragm closes, which completes an electrical circuit that ignites the furnace burners.
If your furnace pressure switch fails or malfunctions, the heating unit won’t turn on. The furnace must have a way to detect the presence of exhaust fumes in the heat exchanger and burner for carbon monoxide prevention. Should the furnace work without a pressure switch, the risk of your home having a potentially deadly carbon monoxide leak would increase dramatically.
Types of Furnace Pressure Switches
Furnace pressure switches can operate using condensing or conventional technology. As such, there are several types of pressure switches to accommodate various heating systems.
For instance, if your home has a single-stage convention furnace, it may have a hose connecting its pressure switch to the draft inducer. On the other hand, a one-stage condensing furnace will use two hoses on the pressure switch to detect pressure on the draft inducer and venting pressure on the condensate collector box.
With a two-stage heating system, you might see dual pressure switches. Modulating furnaces with different heating stages could have three pressure switches to accommodate each heating level.
Most Common Problems With Pressure Switches on Heating Units
The most common and problematic issue with furnace pressure switches is the diaphragm remaining in the open or closed position after the furnace shuts down. The former problem happens more frequently than the latter. The diaphragm is a moving part that’s susceptible to wear and tear as the heating equipment ages.
If the pressure switch diaphragm stays open, it won’t send the electrical signal that ignites the burners. Without functional burners, the furnace won’t produce heat. When the diaphragm sticks in the closed position, your furnace will turn on, but dangerous gases can escape.
A furnace pressure switch could also stop working correctly if the system’s exhaust flue has a clog. A flue obstruction will prevent the inducer motor from generating enough negative air pressure, which means less pressure for the switch to detect.
Troubleshooting and Replacing a Pressure Switch
Many people have furnace issues due to a faulty pressure switch. Unfortunately, testing the switch without the proper experience and tools can be tricky, so calling a qualified HVAC technician is best.
A furnace repair expert can inspect your furnace to uncover its problem. To examine the pressure switch, the professional may use an ohmmeter or voltmeter to measure electrical differences between the switch’s terminals. The switch is bad if the ohmmeter has a reading other than zero or a voltmeter reading lower or higher than 24 and 28 volts DC.
If your furnace pressure switch fails, the HVAC technician can quickly replace it. They’ll also test your furnace to ensure it’s functional after the replacement.
Experience Quality Furnace Services From Canton's Best HVAC Contractor
Now that you know the answer to, “What does a pressure switch do on a furnace?” turn to Green Energy Mechanical Inc. for your heating and cooling needs. Our crew has years of experience meeting the needs of our Canton, Massachusetts, customers while exceeding all expectations. We’re proud to be ENERGY STAR-certified with an A+ Better Business Bureau rating.
At Green Energy Mechanical Inc., we know how to ensure you get the best results from your new furnace and optimize your current model. Call (877) 564-9279 today to book an appointment with us.
