Lever microswitch, the type used for door and position sensing in appliances

Generic photo: Raimond Spekking · CC BY-SA 4.0

How to test a gas furnace draft pressure switch (electrical and draft checks only)

The pressure switch proves the inducer is pulling enough draft before ignition is allowed. Test it with a meter (24 V across it) and a manometer against the set point printed on the switch. Gas valve, gas pressure and burner work are not covered: refer those to a licensed gas technician.

Cross-checked ~30 min advancedBrands: All

Before you start

Turn off the furnace switch before changing hoses or wires
Live-voltage checks are a caution step: insulated probes, one hand, clips attached before power is restored, stay clear of terminals
Do not jumper the pressure switch to run the furnace: risk of carbon monoxide
Gas valve, gas pressure and burner adjustments are blocked: refer to a licensed gas technician
If you smell gas: no switches, leave, call the gas utility from outside

Diagnostic steps

Unlock all 5 steps with expected values

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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