Furnace Pressure Switch Problems: Diagnosis and Fix Guide

The pressure switch is a small, inexpensive safety device that causes a disproportionate number of furnace headaches. When it fails or cannot close properly, your furnace will not fire — period. Understanding how it works and what causes problems helps you troubleshoot effectively and avoid paying for unnecessary repairs.

What the Pressure Switch Does

The pressure switch is a normally-open switch that closes when it detects negative pressure (vacuum) created by the inducer motor. Its job is simple but critical: verify that the inducer motor is running and creating proper draft before allowing gas to flow. If the exhaust path is blocked or the inducer is not working, the pressure switch stays open and the gas valve never receives power. This prevents combustion gases from accumulating inside the furnace and your home.

High-efficiency condensing furnaces often have two pressure switches — one for each stage of combustion. Single-stage 80% AFUE furnaces typically have one. The switches are connected to the inducer housing or collector box via small rubber or silicone hoses.

Symptoms of Pressure Switch Problems

Furnace Starts Inducer But Never Lights

You hear the inducer motor start and run, but the igniter never glows and the burners never light. The control board is waiting for the pressure switch to close, but it never does. After 30-60 seconds, the board gives up and displays an error code — typically 2 blinks on Goodman furnaces.

Furnace Lights Then Shuts Off Quickly

If the pressure switch closes initially but then reopens during the heating cycle, the furnace will shut down mid-cycle. This intermittent behavior often indicates a marginal draft condition — the inducer is barely creating enough vacuum to keep the switch closed.

Error Code Indicates Pressure Switch Fault

Most modern furnaces clearly identify pressure switch errors. Goodman uses 2 blinks for pressure switch open and 3 blinks for pressure switch stuck closed. Check the error code chart on the inside of your blower compartment door for your specific model.

Common Causes (Most Are Not the Switch Itself)

1. Blocked Exhaust Vent — The Minnesota Special

In Minnesota winters, the number one cause of pressure switch problems is a blocked PVC exhaust vent. Ice builds up around the vent termination outside your home. Snow drifts can bury it. Bird nests from the previous season block it. When the exhaust cannot exit, the inducer cannot create proper draft, and the pressure switch stays open. Go outside and check your vent before doing anything else. This takes 30 seconds and solves the problem more than half the time.

2. Blocked or Cracked Pressure Hose

The small rubber hose connecting the pressure switch to the inducer housing can crack, develop holes, or fill with condensation. Any breach in this hose prevents the switch from sensing the vacuum properly. Inspect the hose for cracks, kinks, or water. Replace it if damaged — it is a $3 part from any hardware store.

3. Condensate Drain Clog

In condensing furnaces, a clogged condensate drain causes water to back up into the inducer housing and collector box. This water partially blocks the exhaust path, reducing draft below the threshold needed to close the pressure switch. Clear the condensate drain and trap, then test the furnace.

4. Failing Inducer Motor

An inducer motor with worn bearings may run but not generate enough vacuum to close the pressure switch. The motor sounds like it is running but it has lost performance. This is a motor replacement, not a pressure switch replacement.

5. Actual Pressure Switch Failure

The switch itself can fail — the diaphragm inside can crack or stiffen, or the electrical contacts can corrode. But this is less common than the other causes listed above. Before replacing the switch, rule out everything else first.

How to Test a Pressure Switch

With the furnace calling for heat and the inducer running, use a multimeter set to continuity or resistance. Disconnect one wire from the pressure switch and test across the switch terminals. A closed switch reads near 0 ohms (continuity). An open switch reads infinite resistance. If the inducer is running and the switch reads open, either the draft is insufficient (check the vent and hose first) or the switch is failed.

You can also temporarily bypass the switch by jumpering across its terminals with a short wire. If the furnace lights and runs normally with the switch bypassed, the switch is the problem. However, never leave a pressure switch bypassed — it is a critical safety device. Use the bypass test only for diagnosis, then install a new switch immediately.

Replacement Cost

A pressure switch itself costs $15-$40. It mounts with one or two screws and connects with a push-on electrical connector and a rubber hose. Total replacement time is under 10 minutes. Yet HVAC companies commonly charge $150-$300 for this repair because of the service call fee, diagnostic charge, and parts markup. This is one of the easiest and most affordable DIY furnace repairs.

When ordering a replacement, match by your furnace model number to ensure you get the correct pressure rating. Different furnace models require switches calibrated to different vacuum levels depending on their venting configuration.

Prevention

Prevent pressure switch problems in Minnesota by checking your exhaust vent monthly during winter, keeping the condensate drain clear, and scheduling annual maintenance that includes inducer motor inspection. A $0 vent check in December prevents a $200 emergency service call in January.

If pressure switch problems keep recurring despite addressing the root causes, it may indicate a more fundamental issue with the furnace venting design or an inducer motor that is losing performance. On an older furnace, recurring pressure switch problems combined with other issues may point toward replacement. At Furnace Direct, we sell Goodman furnaces at factory-direct pricing with same-day delivery to the Twin Cities metro. No middleman markup, full factory warranty.