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HVAC systems are complex, with each component performing an essential function. When one mechanism stops working, it affects the whole home’s comfort. One such component is the furnace pressure switch, for which switch failure risks poisonous gas buildup that can infiltrate your home.
What causes a furnace pressure switch to fail? Leith Heating & Cooling, one of the leading HVAC companies in Elgin, Illinois, supplies an answer below. The team also guides you through the troubleshooting process for a furnace pressure switch so that you can determine whether you need to call for professional repair services.
What Does a Furnace Pressure Switch Do?
Modern HVAC systems have numerous safety features, of which the pressure switch is one. You can find pressure switches around the inducer motor of a gas furnace.
Air pressure within the inducer motor forces fumes to evacuate the system. However, if the exhaust builds up, it creates negative pressure within the motor. When the switch senses negative pressure, it halts furnace ignition.
When this happens, the furnace may attempt to reboot up to five times before the control board cuts electricity to the inducer motor and the entire system shuts down. At that point, you need another solution to make your furnace operational again.
The switch can also stop operations in other problematic events, such as:
- Detected gas leaks
- Major mechanical issues
- Carbon monoxide leaks and other dangerous substances
Without realizing it, you and your family rely on the pressure switch’s protection.
Pressure Switch Varieties
Specific furnace models have varying numbers of switches and different switch locations. Peruse your manual or the manufacturer’s website to learn about your system. Still, most furnaces will have a combination of the following types of switches:
- Single-stage conventional furnace: A single hose leading to the inducer and pressure switch.
- Single-stage condensing furnace: Two hoses connecting to the switches on the condensing furnaces; one assigned to the inducer and the other measuring vent pressure near the condensate box.
- Two-stage furnace: Two pressure switches.
- Modulating furnace: Three switches (most often).
You’ll need to verify your system type to learn about the possible switch locations.
What Causes a Furnace Pressure Switch to Fail?
Pressure switches fail for myriad reasons, with reputable HVAC technicians able to identify and solve most of these issues. However, some issues indicate the furnace’s slow but inevitable decline. For instance, common reasons for failure include the following:
- Malfunctioning diaphragm: The diaphragm allows the switch to sense pressure levels. It can develop rips or a grimy film, preventing it from sensing the environment appropriately.
- Electric problems: If the surrounding components receive inadequate voltage from electrical connections, they may trigger switch failure.
- Failing inducer motor: The pressure switch relies on information from the inducer motor. This component may malfunction due to a lack of regular maintenance or old age.
- Leaks: A leak in your furnace system may lead to less pressure. The pressure loss will trigger switch closure.
- Clogged vents: The intake and combustion vents play a pivotal role in air circulation. Sometimes, debris blocks airflow, resulting in negative pressure.
- Inaccurate switch readings: Just like any other aging appliance, your furnace only operates correctly if components like the pressure switch measure their surrounding environments accurately.
- Dirty switch: Most furnace mechanisms gather dust and debris from constant air circulation. Dirty components don’t operate as effectively, which can influence other parts.
- Blocked drainage: The condensate drain line needs occasional maintenance to prevent mold, slime, and other debris from creating clogs.
You might determine what causes a furnace pressure switch to fail by troubleshooting the component.
How the Professionals Test the Pressure Switch in Your Furnace
You should always call a trusted HVAC technician if you feel uncertain about the location or identification of any related component or if there’s a need for switch repair. Typically, the heating and cooling professionals will follow the steps below to test your system’s pressure switches.
Collect the Necessary Equipment
The team will gather the tools to facilitate safe troubleshooting protocols, including the following items:
- Flashlight
- Screwdriver
- Switch hose replacement (if the current one looks damaged or dirty)
- Multimeter
Safety Preparation
Next, the team will turn off the gas and electrical supply connected to your furnace. It may have a disconnect switch that takes your unit off the power grid. If not, the technician would probably need to flip the corresponding breaker in your home’s service panel to be safe.
Check for Blockages
The next step would be to remove the outer furnace panels and check the hose connections for damage or dirt. The technician will look for clogs and replace the hose if needed.
Next, the technician will inspect the vent pipe for debris. If they see a blockage, they’ll attend to it because the exhaust fumes need to travel through this pipe to an opening in the roof of your home to escape.
Inspect the Switch
The technician will then carefully remove all wires connected to the switch, using the multimeter to test the switch’s electrical resistance. If the readings clock in around zero, the switch is working. If the multimeter shows higher readings, the technician will likely need to replace the switch.
Run the Furnace
Finally, the furnace needs a test run. It should function well if the following are in place:
- The hose was intact or replaced
- There were no concerning blockages, or the team removed them
- The multimeter provided a reading of zero
The technician will reconnect the switch, replace the panels, restore the gas and power supply, and turn on your furnace. However, if the unit can’t complete a full cycle, Leith Heating & Cooling’s troubleshooting work begins in earnest!
Let Leith Heating & Cooling Inspect Your Furnace
Our technicians know what causes a furnace pressure switch to fail. We’ll protect your home’s climate control, run further tests, or issue reliable repairs because your comfort is our priority!
If your furnace gas valve is bad, reach out to Leith Heating & Cooling at 847-860-7092 for reputable repairs from friendly, experienced technicians.