Gas Furnace / Induced Draft
Pressure Switch Troubleshooting
Step-by-step diagnostic workflow for furnace inducer pressure switch faults — covers tubing, venting, condensate, inducer performance, wiring, and control board interpretation.
Safety Notice
Disconnect power before inspecting wiring. Combustion venting carries CO risk — ensure proper ventilation. Only trained HVAC technicians should diagnose live-voltage and combustion-related faults.
Confirm Call for Heat
Use a meter rated CAT III or higher when measuring line or control voltage.
Set the thermostat above room temperature to initiate a call for heat. Verify 24 VAC is present between R and W at the furnace control board. If no 24 V signal, the issue is upstream of the pressure switch — check thermostat wiring, transformer, and fuse first.
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