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MEDIUM URGENCY

Carrier Code 31 — Pressure Switch Did Not Close

Code 31 (3 short + 1 long flashes)

Pressure switch did not close — blocked vent, bad inducer, or stuck switch.

Brand: Carrier (Also covers Bryant, Payne)  |  Equipment: Gas Furnace

What This Code Means

Code 31 means the pressure switch did not close after the inducer motor started. When the inducer runs, it creates negative pressure that should close the switch. If it doesn't close in 5 minutes, the inducer shuts down for 15 minutes before retrying.

Likely Causes (Ranked)

Most common

Blocked intake or exhaust vent

What: Snow, ice, birds nests, or a disconnected pipe block proper venting.

How to check: Visually inspect the exhaust outlet outside the house.

Fix: Clear the blockage.

Shop parts
Common

Failed inducer motor

What: Inducer doesn't spin or spins too slowly to create the needed pressure.

How to check: Listen for inducer hum or grinding; should run smoothly.

Fix: Replace inducer motor.

Shop parts
Common

Defective pressure switch

What: Switch contacts don't close even when proper pressure exists.

How to check: Tech can test with manometer.

Fix: Replace pressure switch.

Shop parts
Less common

Restricted pressure tubing

What: Water buildup or kinks in the tubing prevent the switch from sensing pressure.

How to check: Inspect rubber/plastic tubing run.

Fix: Clear water, replace tubing.

Diagnostic Steps

  1. Check exhaust outlet outside for blockage
  2. Listen for inducer motor at startup
  3. Inspect pressure switch tubing
  4. Replace switch if other items check out
  5. Call tech for inducer or persistent issues

Frequently Asked Questions

What's the most common cause of Carrier code 31?
Blocked exhaust vent — especially in winter when snow accumulates over outdoor vents.
Can I fix code 31 myself?
Yes — clearing exterior vent blockages is a 5-minute DIY fix. Inducer replacement is professional.
How urgent is code 31?
Not safety-critical, but you'll have no heat until fixed. Same-day attention recommended in winter.

Related Carrier Codes

Carrier Error Code 23Carrier Error Code 33

Related Symptoms

Furnace Not IgnitingFurnace Blowing Cold Air

Need More Help?

Try our interactive symptom diagnostic tool or browse Carrier parts.

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