Furnace Pressure Switch: What It Does, Why It Fails, How to Fix

The pressure switch is one of the most commonly involved components in furnace "won't start" problems. It's a small, inexpensive safety device — but when it fails (or when something else makes it think it has failed), your furnace won't fire. Here's everything Minnesota homeowners need to know.

What Does the Pressure Switch Do?

The pressure switch is a safety device that verifies the draft inducer motor is creating proper negative pressure (suction) before allowing the gas valve to open. Here's the sequence:

1. Thermostat calls for heat
2. Draft inducer motor starts (creates suction through the heat exchanger)
3. Pressure switch detects the suction — "closes" the circuit
4. Control board confirms pressure switch is closed
5. Ignitor energizes
6. Gas valve opens — burner ignites

If the draft inducer isn't pulling enough suction — due to a failed motor, blocked flue, or other issue — the pressure switch stays open, and the furnace won't ignite. This is a safety feature: running a furnace without proper draft could push combustion gases into the home.

Types of Pressure Switches

• Single-stage pressure switch: One switch, one setpoint — found on single-stage furnaces
• Dual pressure switch: Two switches monitoring both stages — found on two-stage furnaces, one for each firing rate
• Inducer pressure switch: Monitors draft inducer suction (most common)
• Vent pressure switch: Some models have a second switch monitoring vent pressure

Common Pressure Switch Error Codes

On Goodman furnaces, pressure switch faults appear as specific LED flash patterns:

See our full Goodman error code guide for all flash patterns.

Why Pressure Switches Fail (and What Actually Causes "Failures")

Here's an important distinction: pressure switches rarely fail by themselves. Most "pressure switch failures" are actually caused by something else making the switch behave correctly — it's detecting a real problem.

Actual Causes of Pressure Switch Issues

1. Clogged condensate drain: The #1 cause in high-efficiency furnaces. Water backing up into the pressure switch hose causes a false "open" reading. The switch is working correctly — it's detecting flooded drainage.
2. Blocked intake or exhaust pipe: Birds, wasps, ice, or debris blocking PVC vent pipes reduces draft, causing the switch to stay open.
3. Failed draft inducer motor: If the inducer isn't spinning properly, insufficient pressure is created.
4. Cracked pressure switch hose: The rubber hose connecting the switch to the inducer cracks or disconnects, losing the pressure signal.
5. Pressure switch out of calibration: The switch itself becomes inaccurate over time and trips at the wrong pressure level.
6. Actual switch failure: The switch's internal diaphragm tears or contacts corrode. This is the least common cause.

Diagnosing Pressure Switch Problems

Step 1: Check the Condensate Drain

For high-efficiency furnaces: is there water backing up near the furnace? Check the drain pan. A clogged condensate drain is the most common cause of pressure switch trips. See our condensate drain guide.

Step 2: Check Intake/Exhaust Pipes

Go outside and look at the PVC pipe terminations. Any obstruction (ice buildup, bird nest, wasp nest, debris)? Clear it and try restarting.

Step 3: Inspect the Pressure Switch Hose

With the furnace off and unplugged, locate the rubber hose running from the draft inducer housing to the pressure switch. Check for cracks, kinks, or disconnected ends. Reconnect or replace (typically $5–$15 at a hardware store).

Step 4: Listen to the Inducer

Restore power and watch/listen when the furnace starts. Does the inducer motor spin up normally? A grinding, squealing, or slow inducer suggests motor failure. See our draft inducer motor guide.

Step 5: Test the Pressure Switch

With a multimeter, test for continuity across the switch terminals when the inducer is running. The switch should close (continuity) when suction is present. If the switch stays open despite normal inducer operation, the switch itself may be faulty.

Pressure Switch Replacement Cost

• Pressure switch part: $15–$60 (many are OEM-equivalent aftermarket)
• Technician diagnosis and replacement: $150–$300 total
• DIY replacement: Possible for mechanically inclined homeowners — match part number, disconnect hose and wires, swap switch, reconnect

When It's NOT the Pressure Switch

Don't replace the pressure switch until you've ruled out the underlying causes listed above. Replacing a switch when the condensate drain is clogged, the vent is blocked, or the inducer is failing will just result in the new switch tripping for the same reason. Fix the root cause first.

Related Resources

• Furnace Not Turning On: Full Diagnostic Checklist
• Goodman Error Codes: Diagnostic Guide
• Draft Inducer Motor: Function and Failure
• Furnace Condensate Drain: Clogs and Fixes
• Furnace Safety Devices: Every Switch Explained