Carrier furnace code 31 (3 short, 1 long): pressure switch

Furnace control LED

31

“PRESSURE SWITCH DID NOT CLOSE OR REOPENED”

58MCB, 58STA/58STX, PG8MAA/PG8JAA, 58SB0A/58SC0A, 810SA, PG80ESAA, 820SA, 59SC5A, 59SP5A · 58MCB-4SM p. 15; 58ST-24SI p. 43; IM-PG8J-17 p. 43; 58SC0A-05SI p. 26; 58SB0A-04SI p. 26; II810SA-05 p. 26; IM-PG80ESA-05 p. 26; IM-PG80ESAA-04 p. 27; II820SA-02 p. 26; 59SC5A-13SI p. 67; 59SP5A-18SI p. 70
Owner checks, then technician

What it means

Code 31 is three short flashes and one long. On most labels it means a pressure switch did not close, or opened again 58SC0A-05SI, p. 26. The switch named depends on the board: just “pressure switch” on several single-stage labels, the HPS on the 59SC2D, 59SC5B and 59SP6A, the high-heat switch or its relay on two-stage boards, the medium or high switch on modulating boards, and a pressure transducer reading on ultra low NOx models (see the notes below). The causes the labels list concern the vent and combustion air, the inducer motor, the pressure tubing and the switch itself 58SC0A-05SI, p. 26; 59SC5B-04SI, p. 63.

On the 58SB0A and 58SC0A label, if the switch stays open longer than five minutes, the inducer shuts off for 15 minutes before the control tries again; the 58MCB, 58STA and 820SA labels say the same 58SC0A-05SI, p. 26; 58MCB-4SM, p. 15; 58ST-24SI, p. 43; II820SA-02, p. 26. On the 59SC2D, 59SC5B and 59SP6A, if the HPS stays open for one minute after the gas valve closes, after three successive trials, the control locks out for 3 hours before it retries; the 59SC5A and 59SP5A labels give the same rule for their HPS 59SC5B-04SI, p. 63; 59SC5A-13SI, p. 67. On two-stage and modulating boards the 31 label refers you to code 32 for the causes 58TN0A-02SI, p. 35; 59TP6A-10SI, p. 73.

Check these first

The owner’s manuals do not name code 31. The service label lists a restricted vent and excessive wind among its causes 58SC0A-05SI, p. 26; 59SC5B-04SI, p. 63; 59SU5A-05SI, p. 51; on two-stage boards these items are in the 32 list instead, as the code 32 page shows 58TN0A-02SI, p. 35. Carrier’s owner’s manual for condensing furnaces lets you check the outside end of the vent and the air intake:

1. Write the code down before you turn off the power or remove the blower access door OM9GFRC-02, p. 10. Carrier’s 80% owner’s manual does not mention the LED. How to count the flashes: reading a Carrier code.
2. Check for obstructions around the vent termination OM9GFRC-02, p. 11. The manual asks that the vent and air intake terminals not be obstructed in any way during all seasons OM9GFRC-02, p. 3.
3. Check the combustion-air intake next to the furnace or outside your home for blockage OM9GFRC-02, p. 9. The labels list inadequate combustion air supply among the causes 58SC0A-05SI, p. 26.
4. If you find holes in the vent pipe, or it is obstructed or not connected, the manual says: “DO NOT OPERATE YOUR FURNACE. Call your dealer for service.” OM9GFRC-02, p. 9. Carrier’s 80% manual prints the same warning 80GSFRN-C-03OM, p. 7; its checklist has no vent item.
5. If the furnace still fails to operate, call your service representative OM9GFRC-02, p. 11.

When to call a licensed technician

• The rest of the label’s list: vent sizing, a defective inducer motor, low inducer voltage (115 VAC), a defective pressure switch, disconnected or obstructed pressure tubing, and low inlet gas pressure (if LGPS used) 58SC0A-05SI, p. 26.
• On the condensing 59SC5A, 59SP5A, 59SC2D, 59SC5B and 59SP6A, restricted or blocked condensate drainage 59SC5A-13SI, p. 67; 59SC5B-04SI, p. 63.
• On the 59SU5A, Bryant 935SA and 59CU5A, a defective pressure transducer and a frozen or blocked drain 59SU5A-05SI, p. 51; 59CU5A-01SI, p. 65.
• On two-stage boards, the control relay, which the label says may be defective; the 59TN6B, 986TC, 58MVP and TG-GFC80-02 labels add a mis-wired gas valve 58TN0A-02SI, p. 35; 59TN6B-01SI, p. 60; 58-06T, p. 7; TG-GFC80-02, p. 7.
• The owner’s manual lets untrained people clean and replace air filters and says all other operations must be performed by trained service personnel OM9GFRC-02, p. 2.

Notes for different models

• “PRESSURE SWITCH DID NOT CLOSE OR REOPENED”: 58MCB, 58STA and Payne PG8MAA, 58SB0A, 58SC0A, Bryant 810SA and Payne PG80ESAA, Bryant 820SA, 59SC5A and 59SP5A 58MCB-4SM, p. 15; 58ST-24SI, p. 43; 58SC0A-05SI, p. 26; II820SA-02, p. 26; 59SC5A-13SI, p. 67; 59SP5A-18SI, p. 70. The 59SC5A and 59SP5A labels have no 32: their 31 covers both the low and the high pressure switch 59SC5A-13SI, p. 67; 59SP5A-18SI, p. 70.
• “HPS PRESSURE SWITCH DID NOT CLOSE OR REOPENED”: 59SC2D, 59SC5B and 59SP6A; on these, 32 is the LPS 59SC2D-02SI, p. 61; 59SC5B-04SI, p. 63; 59SP6A-01SI, p. 59.
• “HIGH-HEAT PRESSURE SWITCH OR RELAY DID NOT CLOSE OR REOPENED”: 58TP0A, 58TN0A and Bryant 880TA, 59TN6B and Bryant 986TC, 58MVP, and the TG-GFC80-02 guide 58TP0A-02SI, p. 37; 58TN0A-02SI, p. 35; 59TN6B-01SI, p. 60; 58-06T, p. 7; TG-GFC80-02, p. 7. The 59TP6A, 59TP6B and Payne PG96VAT label says “OR HPSR RELAY” 59TP6A-10SI, p. 73.
• “MEDIUM PRESSURE SWITCH, HIGH PRESSURE SWITCH OR PSR RELAY DID NOT CLOSE OR REOPENED”: the modulating 59MN7B and 59MN7A 59MN7B-02SI, p. 73; 59MN7A-01T, p. 8.
• “PRESSURE TRANSDUCER INPUT DOES NOT SENSE TARGET PRESSURE OR PRESSURE IS OUT OF RANGE”: 59SU5A, Bryant 935SA, 59CU5A and Payne PG80ESU 59SU5A-05SI, p. 51; 59CU5A-01SI, p. 65; GFULN80-G-01TS, p. 6.
• The 58PAV and 58RAV Series 131 label reads “PRESSURE, DRAFT SAFEGUARD, OR AUXILIARY LIMIT (when used) SWITCH DID NOT CLOSE OR REOPENED” and lists vent restriction or high winds 58P_R-9SM, p. 9.
• On 3-digit displays: 31.1 is “Pressure switch open” on the 58SP0B and “Open Main pressure switch.” on the Bryant 800SB 58SP0B-01SI, p. 30; II800SB-01, p. 31; 31.6, “Open secondary pressure switch (HPS)”, and 31.7, high heat only for the next cycle because the HPS failed to close in 75 seconds when changing from low to high heat, are on the 59TP6C, 59TP7A, Bryant 926TC and Payne PG96VTAB 59TP6C-01SI, p. 56; IM-PG96VTAB-01, p. 54; 31.4 and 31.5, loss of pressure before or after the blower comes on, are on the Bryant 935SB II935SB-01, p. 48. Codes 31.2 and 31.3 do not appear in any of these tables.
• The 58SU0A has no 31; its pressure faults are 2 and 3 red flashes 58SU0A-05SI, p. 36.

Related Carrier codes

• 32 “LOW-HEAT PRESSURE SWITCH DID NOT CLOSE OR REOPENED”
• 23 “PRESSURE SWITCH DID NOT OPEN”
• 43 “LOW-HEAT PRESSURE SWITCH OPEN WHILE HIGH-HEAT PRESSURE SWITCH IS CLOSED”
• 31.1 “Pressure switch open”

See also

• Heat pump vs gas calculator
• HVAC and furnace tax credits in 2025 and 2026: 25C, 25D, 30C

Other gas furnaces: Goodman, Lennox, Rheem and Ruud

All Carrier codes

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