Carrier Furnace Code 23: Pressure Switch Did Not Open

Last updated Sep 15, 2026 · By fixme.vip Editorial

Carrier furnace code 23: what it means

Carrier Furnace Code 23 means the pressure switch did not open — the switch contacts were already closed at the start of the heating cycle, before the inducer (draft) motor started.

Under normal operation, the pressure switch should be open when the furnace is at rest, then close once the inducer motor spins up and creates the correct draft. The control board watches for that sequence. If the switch is closed while the inducer is still off, the board can’t verify that the switch is working as a genuine safety proof of draft — so it flags Code 23 and won’t allow ignition.

This is a control-circuit safety fault, not a gas or flame problem. The furnace is protecting itself: if a stuck-closed switch were allowed to fool the board, the furnace could fire without proper venting. On most Carrier boards this fault re-checks every startup — it clears when the switch behaves correctly but will keep reappearing until the underlying stuck switch or wiring is repaired.

Carrier furnace code 23: common causes, ranked by probability

1. Pressure switch stuck closed — the most common cause. Contacts inside the switch weld or stick shut and never open at rest.
2. Shorted or pinched switch wiring — a wire chafed against sheet metal or a damaged connector shorts the circuit, mimicking a closed switch.
3. Failed/degraded pressure switch — an aging switch whose diaphragm or contacts no longer reset to the open position.
4. Incorrect switch or wrong pressure rating installed — after a prior repair, a mismatched switch may not open at the expected setpoint.
5. Moisture or debris inside the switch — condensate or dirt holding the contacts closed (more common on high-efficiency condensing models).

Note: causes like blocked vent piping or a clogged condensate trap typically produce a switch that won’t close (Code 31), not one that won’t open. Code 23 is specifically the opposite failure — a switch stuck in the closed position.

How to fix Carrier furnace code 23: safe checks first

These are the only steps a homeowner should do. Everything else on this fault is inside the cabinet and is technician work.

• Thermostat: Confirm it’s set to Heat and the target temperature is above room temperature. Replace the batteries if it’s battery-powered.
• Air filter: Check and replace a dirty filter. A clogged filter won’t cause Code 23 directly, but it’s good practice and rules out airflow confusion.
• Breaker / furnace switch: Cycle the furnace breaker off and on once, and confirm the service switch on or near the furnace is on. This gives the board one clean restart.
• Visible vents and registers: Make sure supply and return vents in your home aren’t blocked by furniture or rugs.
• Condensate drain (condensing models): If you see standing water or a full condensate pan, check that the drain line isn’t obviously clogged or kinked.

Do not open the furnace cabinet, remove or bypass the pressure switch, or disconnect its tubing. If Code 23 returns after one reset, call a technician.

How a technician will diagnose it

A qualified HVAC tech will confirm the fault with a systematic check so you can sanity-check any quote:

1. Read the code history on the control board LED to confirm Code 23 versus a related pressure-switch code.
2. Measure the pressure switch at rest with a multimeter — a properly working switch reads open with the inducer off. A closed reading confirms the stuck switch.
3. Inspect the wiring and connectors from the switch to the board for shorts, chafing, or pinched wires against sheet metal.
4. Verify the switch spec matches the furnace model and its pressure rating (important after prior repairs).
5. Check for moisture or debris in the switch body and its hose (common on condensing units).
6. Test the sequence by watching the switch open at rest and close when the inducer runs, confirming the repair.

Symptom, cause and what to do

Carrier furnace code 23 repair cost

Honest US ranges. Actual pricing varies by region, model, and access.

• Homeowner reset / no parts: $0 if a clean restart clears a transient fault.
• Diagnostic / service call: $90 – $180 typical, often credited toward the repair.
• Pressure switch replacement: $150 – $350 including parts and labor. Condensing-model switches and dual/triple switch assemblies sit at the higher end.
• Wiring repair (shorted/pinched harness): $120 – $300 depending on how much harness must be replaced.
• Cleaning moisture/debris from switch and hose: $100 – $200 if the switch itself is still good.

Because every documented fix here is inside the cabinet, this is a pro repair. Beware quotes that jump straight to a full control board or inducer replacement without first testing the switch and wiring.

Related codes

• Carrier Furnace Code 31: Causes, Fixes & Costs — the opposite pressure-switch fault, where the switch won’t close (blocked vent, condensate, or weak inducer).
• Carrier Furnace Code 33: Causes, Fixes & Costs — limit or flame-rollout related faults.
• Carrier Furnace Code 34: Ignition Proving Failure & Fixes — for ignition and flame-proving issues.
• Carrier Furnace Code 22: Abnormal Flame-Proving Signal — flame-sensing circuit faults.
• Carrier Furnace Code 12: Meaning, Causes & Fixes — control/power-related startup faults.