Mike PleziaInside service technician, Clark Associates · Commercial Equipment, HVAC, and Refrigeration professional

Pressure Switch: The Switch Isn't the Problem

7 Oct 2026 · 1 min

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0:57

In this instructional video, the speaker addresses HVAC technicians, especially newcomers, explaining that the furnace pressure switch is a safety device that confirms the inducer motor is creating sufficient negative pressure to vent combustion gases. When the inducer fails to generate enough draft—due to a blocked vent pipe, a dirty inducer wheel, or a weak motor—the pressure switch opens, shutting down the furnace before gas is introduced. The speaker cautions against the common mistake of immediately replacing the switch when a fault appears. Instead, he advises a systematic upstream diagnostic: inspect the vent pipe for obstructions, check the condensate drain on high‑efficiency units, and manually spin the inducer to assess drag. The key message is that the pressure switch is usually functioning correctly and is signaling an upstream issue.

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Hey, are you new to the trades? Here's something you may not know about pressure switches in a gas furnace. The pressure switch is a safety device. It proves that the inducer motor is running and creating enough negative pressure to safely vent combustion gases out of the heat exchanger. If the inducer isn't pulling enough draft— maybe the venting is blocked, the inducer wheel is dirty, or the motor is weak— the switch opens and shuts the furnace down before gas ever flows. A lot of new techs see a pressure switch fault and immediately assume it's a bad switch. But the switch is usually doing its job. Start upstream. Check the vent pipe for blockage, check the condensate drain if it's a high-efficiency furnace, and spin the inducer by hand to feel for drag. The switch isn't the problem— it's telling you there is one. Now that you know, you can help someone else know!