Replace a Pressure Switch (Furnace)

Find the real cause first — a blocked sensing port, plugged condensate trap, or restricted vent is more common than a failed switch — then match the setpoint ("WC) and the normally-open config, install, and verify it closes on inducer start. Never jumper a pressure switch to run the furnace.

Approx. 40 min

Before you start

•Switch confirmed as the actual fault: with the inducer pulling rated draft and ports/tubing/vent/trap CLEAR, the switch still won't close (or won't open) — proven with a manometer and a meter, not assumed.
•Replacement switch that matches the OEM setpoint (e.g. specific "WC), the contact configuration (normally-open, single vs dual), and the port/fitting style.
•Power can be killed at the furnace switch and a manometer/meter is available.

Tools & materials

Multimeter (continuity across the switch) · Manometer / draft gauge (verify actual pressure vs setpoint) · Nut drivers/screwdrivers · Replacement OEM pressure switch (matched "WC + config)

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Diagnose the real cause first

Check ports, tubing, trap, and vent before condemning the switch
The most common 'bad pressure switch' is actually a blocked sensing port, cracked/plugged tubing, a full condensate trap, or a restricted vent/intake. Clear and verify those first — replacing the switch won't fix a draft restriction.
Target: Sensing port, tubing, condensate trap, and vent/intake all verified clear
Never jumper the pressure switch
Do not jumper or tape a pressure switch closed to 'make it run'. It's a safety that proves the inducer is moving combustion products; defeating it can let the furnace fire with blocked venting and spill CO.
⚠ NEVER jumper a pressure switch — it is a combustion-safety device; defeating it risks CO spillage.

Match & install

Match setpoint and configuration
Read the old switch's setpoint ("WC) and contact config (normally-open, single or dual) off its label and match it exactly. A wrong setpoint either nuisance-trips or fails to protect.
Target: Match "WC setpoint, N.O. config, and port style to OEM
Mount and reconnect to the correct port
Lock out power, mount the new switch, and reconnect the sensing tube(s) to the correct port(s). Don't pinch or route tubing where it can trap condensate.
⚠ Verify 0 V before working on the leads.

Verify closure on draft

Confirm it closes on inducer start
Restore power, call for heat, and confirm the switch closes once the inducer establishes draft (meter across it, or the sequence advances to ignition). Compare actual pressure on the manometer to the switch setpoint.
Tools: Multimeter, Manometer
Target: Closes when measured draft meets/exceeds the setpoint; sequence advances