What Happens When a Furnace Pressure Switch Goes Bad

What happens when a furnace pressure switch goes bad? DEAR Services provides expert furnace repair services in Yelm, WA, and passionately educates homeowners about warning signs and the benefits of prompt service. Keep reading to discover everything you should know about pressure switches.

What Does the Furnace Pressure Switch Do?

The pressure switch functions as a safety component that turns off the furnace when it detects dangerous conditions within the device, such as a lack of negative pressure. Though electric and gas heating systems require different fuel sources, they both still contain a pressure switch. When a furnace doesn’t turn on, an HVAC professional can determine whether you should blame the switch.

Troubleshooting a Bad Switch

How can a homeowner know when they have a faulty pressure switch? The furnace will attempt to start up multiple times, with several minutes of rest between each cycle. After three to five attempts, if the switch hasn’t engaged, the furnace enters safety lockout mode.

Some modern furnaces make the diagnosis process easy. They have an LED or error code that identifies the switch as the source of the problem. If you don’t hear a click when the furnace starts, you have another indication of a faulty safety component.

Most Frequent Causes of Faulty Pressure Switch

What happens when a furnace pressure switch goes bad? Several common conditions can cause the problem.

Wear and Tear From Aging

Over time, the pressure switch can corrode or experience damage. On average, it should last about 50,000 cycles, which equates to several years. The less a family uses their heating system, the longer they can avoid replacing this component.

Electrical Problems and Shorts

Various electrical problems can cause the switch to malfunction. For example, a loose electrical connection may not provide the power the component needs or may become unreliable at best.

A power surge could also damage the piece. For example, it could short out the wires and prevent them from working properly.

A Damaged Hose or Diaphragm

The pressure switch contains a diaphragm or bellow that responds to changes in pressure as the furnace activates. If this component experiences damage, the switch can’t sense the conditions of the heating system and shuts everything down.

The suction hose connects the switch to the combustion chamber. It further helps the inducer fan communicate with the safety feature. If the hose disconnects or becomes damaged, it can cause problems in the system.

Inducer Motor or Fan Malfunctions

When the thermostat activates your furnace, the inducer fan turns on and creates a space of negative pressure. This draws in the combustion gases and tells the pressure switch that the furnace can safely ignite. Without this pressure difference, lighting the device can cause a dangerous buildup of carbon monoxide.

What causes problems with the fan or motor?

• Sluggish operation
• Poor electrical connections
• Blockages
• Dirt buildup
• Damage
• Excess moisture

Blockages in Ventilation

A flue blockage is often behind what happens when a furnace pressure switch goes bad. The furnace connects to a flue or chimney to expel the unused gas and combustion byproducts. 

A blocked flue can cause serious issues, such as carbon monoxide leaking into the home. It can also raise the pressure inside the furnace, preventing the inducer from creating the correct conditions.

Leaking Exhaust Gases

If the furnace’s safety features detect leaking carbon monoxide or natural gas, they’ll shut the system down to prevent dangerous conditions. What symptoms of this deadly gas should homeowners watch for?

• Headache, hallucinations, and visual disturbances
• Fatigue, weakness, and confusion
• Abdominal pain, nausea, and vomiting
• Palpitations and agitation
• Shortness of breath
• Seizures

Addressing a Furnace’s Malfunctioning Switch

What should you do when a pressure switch malfunctions? Turn the furnace off and call for immediate repairs.

You can’t use the furnace until a certified technician completes the repairs. The winter conditions in Yelm grow dangerously cold, so don’t delay restoring your heat.

With proper care, homeowners can prolong the need to repair or replace this component. An annual inspection goes a long way toward keeping every part of a heating system in excellent condition.

Running the furnace in moderation also helps. The U.S. Department of Energy suggests keeping furnaces at 68 degrees Fahrenheit in the winter.