Carrier furnace code 33 (3 short, 3 long): limit circuit fault

Furnace control LED

33

“LIMIT CIRCUIT FAULT”

Printed on 17 model series · 26 documents

58MCB, 58STA/58STX, PG8MAA/PG8JAA, 58SB0A/58SC0A, 810SA, PG80ESAA, 820SA, 58TP0A, 58TN0A, 880TA, 59SC2D, 59SC5A, 59SP5A, 59SC5B, 59SP6A, 59TP6A/59TP6B, PG96VAT, 59TN6B, 986TC, 59MN7B, Guide TG-GFC80-02 (models not listed), 59MN7A Series 100, 58MVP/58MVB/58UVB · 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; 58TP0A-02SI p. 37; 58TN0A-02SI p. 35; II880TA-02 p. 35; 59SC2D-02SI p. 61; 59SC5A-13SI p. 67; 59SP5A-18SI p. 70; 59SC5B-04SI p. 63; 59SP6A-01SI p. 59; 59TP6A-10SI p. 73; 59TP6B_04SI p. 67; IM-PG96VAT-13 p. 70; 59TN6B-01SI p. 60; II986TC-01 p. 60; 59MN7B-02SI p. 73; TG-GFC80-02 p. 7; 59MN7A-01T p. 9; 58-06T p. 8

Owner checks, then technician

What it means

Code 33 is three short flashes followed by three long ones. Most Carrier, Bryant and Payne labels call it “LIMIT CIRCUIT FAULT” and explain it as a limit or flame rollout switch that is open 59SC5A-13SI, p. 67. On the 58STA, 58SB0A, 58SC0A, 820SA, 58TP0A and 58TN0A families the label adds the draft safeguard and a blocked vent switch, if used 58SC0A-05SI, p. 26; 58TN0A-02SI, p. 35.

While the switch is open, the blower runs for 4 minutes or until the switch closes again, whichever is longer. If the switch stays open longer than 3 minutes, the code changes to 13, a lockout; if it closes sooner, 33 keeps flashing until the blower stops 59SC5A-13SI, p. 67. On two-stage boards, 33 can also mean the furnace is running in high heat only after 2 successive low-heat limit trips 59TP6A-10SI, p. 73; 58TN0A-02SI, p. 35. The owner’s manual says the rollout switch shuts the furnace off after high temperature conditions, and that a dirty filter can make the furnace overheat and shut down automatically OM9GFRC-02, pp. 7, 11.

Check these first

Carrier’s owner’s manuals have no code table. The steps below come from their general checklist, “Before you request a service call”, and only where the 33 label names the same cause.

1. Write the code down before you turn off the power or remove the blower access door, as Carrier’s owner’s manual for condensing furnaces asks 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. The label lists “Dirty filter or restricted duct system” among the causes 59SC5A-13SI, p. 67. The owner’s manual lets you check for a dirty air filter and for return-air or supply-air grilles that are blocked or closed OM9GFRC-02, pp. 10–11; 80GSFRN-C-03OM, p. 7. It asks for the filter to be checked every four weeks and cleaned or replaced if necessary OM9GFRC-02, p. 7.
3. The label also says the flame rollout switch requires a manual reset 59SC5A-13SI, p. 67. The owner’s manual gives you that step, behind the furnace door. First turn off the electrical power supply to the furnace and install a lockout tag before removing the access doors OM9GFRC-02, p. 10; Carrier’s 80% manual says to turn off the electrical power supply before removing the access doors 80GSFRN-C-03OM, pp. 5, 7. On condensing furnaces the manual names a manual reset rollout switch on the burner box: push the button on the switch, and if it trips again, shut down the furnace and call for service OM9GFRC-02, p. 11. Carrier’s 80% manual names manual reset limit switches on the ends of the burner enclosure, which trip after a high-temperature condition due to inadequate combustion air; push the button, and if a switch trips a second time, turn off the furnace and call for service 80GSFRN-C-03OM, p. 7. The 80% manual does not use the word rollout; this page treats those switches as the ones the label calls the flame rollout switch.
4. The manual’s start-up steps replace the main furnace door before the electrical supply is turned on OM9GFRC-02, p. 5, steps 7 and 8.
5. If the furnace still fails to operate, call your service representative OM9GFRC-02, p. 11.

The 33 labels of the 59TP6A, 59TP6B and Payne PG96VAT, the 59TN6B and Bryant 986TC, the 59MN7B and the 58MVP do not list the filter; their causes are in the technician list below 59TP6A-10SI, p. 73; 59TN6B-01SI, p. 60; 59MN7B-02SI, p. 73; 58-06T, p. 8. Their labels still say the flame rollout switch requires a manual reset.

When to call a licensed technician

• The rollout or limit switch trips again after you push the button OM9GFRC-02, p. 11; 80GSFRN-C-03OM, p. 7.
• The code turns into 13, or the furnace still fails to operate after the checklist 59SC5A-13SI, p. 67; OM9GFRC-02, p. 11.
• The other causes on most labels: a loose blower wheel, a defective blower motor or capacitor, a defective switch or its connections, a restricted vent, vent sizing, excessive wind, and inadequate combustion air supply when the flame rollout switch is open 59SC5A-13SI, p. 67; 58SC0A-05SI, p. 26.
• On the 59TP6A, 59TP6B, PG96VAT, 59TN6B, 986TC and 59MN7B the list reads differently: an improper limit switch or no limit gasket, a defective switch or connections, the gas input adjustment, a loose blower wheel, and on the two-stage models a stuck high-heat solenoid in the gas valve 59TP6A-10SI, p. 73; 59TN6B-01SI, p. 60; 59MN7B-02SI, p. 73. The 58MVP guide also names the rear air baffle and an improper or misaligned limit or limit shield 58-06T, p. 8.
• 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

• The 58PAV and 58RAV Series 131 label calls 33 “LIMIT OR FLAME ROLLOUT SWITCH IS OPEN” and lists an open flame rollout switch with manual reset among the causes 58P_R-9SM, p. 9.
• The labels of the 58STA, 58SB0A, 58SC0A, 820SA, 58TP0A and 58TN0A families say the flame rollout switch and the BVSS require manual reset 58SC0A-05SI, p. 26; 58TN0A-02SI, p. 35. The 80% owner’s manual shows a blocked vent switch in its component drawings 80GSFRN-C-03OM, p. 2 but gives no reset step for it; its only manual-reset instruction is for the limit switches on the burner enclosure 80GSFRN-C-03OM, p. 7.
• On the modulating 59MN7B, 33 also covers running in maximum heat after 2 successive low or medium range limit trips 59MN7B-02SI, p. 73; the 59MN7A guide words it as 2 successive limit trips at 71% of maximum rate or less 59MN7A-01T, p. 9.
• The 59SU5A, Bryant 935SA, 59CU5A and Payne PG80ESU labels have no 33; an open limit gives code 13 there 59SU5A-05SI, p. 51; 59CU5A-01SI, p. 65; GFULN80-G-01TS, pp. 6–7.
• Boards with a 3-digit display show 33.1, “A switch has opened in the Main Limit circuit.” on the 59TP6C, 59TP7A, Bryant 926TC, Payne PG96VTAB and Bryant 800SB, and “Main Limit circuit open” on the 58SP0B. The two-stage 3-digit boards add 33.2, “Lockout - High Heat Only for current cycle” 59TP6C-01SI, p. 56; IM-PG96VTAB-01, p. 54; 58SP0B-01SI, p. 30; II800SB-01, p. 31. The Bryant 935SB table has no 33 II935SB-01, p. 48.
• The 58SU0A shows an open main limit circuit as 4 red flashes; its checks include a dirty filter and blockages in the flue pipe 58SU0A-05SI, p. 36.
• The Infinity zone control lists furnace code 33 as “Limit Circuit Fault AND high heat only is active” UIZ01-07SI, p. 20.

Related Carrier codes

• 13 “LIMIT CIRCUIT LOCKOUT”
• 33.1 “A switch has opened in the Main Limit circuit.”
• 33.2 “Lockout - High Heat Only for current cycle”
• 4 red flashes “Main Limit Circuit 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

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