What does Carrier code 31 mean?
Carrier furnace code 31 means the high-heat pressure switch or relay did not close, or reopened during operation on the supported control family. Confirm the model number and diagnostic chart inside the furnace door before replacing parts.
What causes Carrier code 31?
- A blocked intake or exhaust vent
- A restricted condensate drain or pressure hose
- A weak inducer motor or pressure switch
Can I troubleshoot Carrier code 31?
- With the furnace off, check outdoor intake and exhaust openings for snow, ice, leaves, or nests.
- Replace a visibly dirty air filter, restore power once, and note whether the code returns.
How much does Carrier code 31 cost to fix?
A pressure switch replacement typically costs between $175 and $900 nationally.
When should I call a technician?
Call a technician if the vent is clear and the pressure-switch code returns; combustion-air testing requires instruments.
Symptoms this code causes
Sources and model scope
Fault codes vary by model and control board. Confirm the diagnostic chart inside your furnace panel or the official manual before acting.
Scope used here: Carrier-family two-stage controls covered by troubleshooting guide 58-3T.
- Carrier Corporation: Deluxe 2-Stage Gas-Fired Induced-Combustion Furnaces — Troubleshooting Guide
58-3T · Carrier-family two-stage furnace controls covered by document 58-3T; codes vary on other boards and model generations.
Compiled by Warmlo Editorial · Reviewed August 2026
This is general information, not professional advice. Gas, electrical, and combustion repairs can be dangerous — when in doubt, call a licensed technician.