HVACopediaCarrier · Furnace
33 Limit circuit fault
What the control is telling you
The limit or a flame rollout switch is open, or the furnace is in high-heat-only mode after 2 successive low-heat limit trips. Blower runs at least 4 minutes; if open over 3 minutes the code becomes lockout 13.
Applies to: 59TP6A two-stage variable-speed ECM multipoise condensing gas furnace, all sizes (040-10 to 120-22)
Likely causes
- Loose blower wheel
- Defective switch or connections
- Improper low- or high-heat gas input
- Wrong limit switch or no limit gasket
- Dirty filter or restricted ducts
- Open flame rollout switch (manual reset)
Test and repair steps
- Warning: Shut off 115-V power and gas, and lock/tag out before working inside the furnace; there may be more than one power source.
- Replace dirty filters and check supply/return ducts for restrictions.
- Check the blower wheel is secure.
- Check gas input by clocking the meter and manifold pressure in both stages.
- Inspect the limit switch, its gasket and wiring; replace if defective or incorrect.
- If the rollout switch is open, correct combustion air, gas pressure, burner/orifice alignment or venting before manually resetting it.
- Verify temperature rise is within the rating-plate range after repair.
Settings for these units
Filter sizes by casing width and filter cabinet · 59TP6A
| Location | Size | Side return filter | Bottom return filter | Type |
|---|---|---|---|---|
| Furnace casing | 14-3/16 in. wide | 16 x 25 x 3/4 in. | 14 x 25 x 3/4 in. | Washable |
| Furnace casing | 17-1/2 in. wide | 16 x 25 x 3/4 in. | 16 x 25 x 3/4 in. | Washable |
| Furnace casing | 21 in. wide | 16 x 25 x 3/4 in. | 20 x 25 x 3/4 in. | Washable |
| Furnace casing | 24-1/2 in. wide | 16 x 25 x 3/4 in. | 24 x 25 x 3/4 in. | Washable |
| Filter cabinet | 16 in. high | (1) 16 x 25 x 3/4 in. or (1) 16 x 25 x 4-5/16 in. | - | Washable or media |
| Filter cabinet | 20 in. high | (1) 20 x 25 x 3/4 in. or (1) 20 x 25 x 4-5/16 in. | - | Washable or media |
| Filter cabinet | 24 in. high | (1) 24 x 25 x 3/4 in. or (1) 24 x 25 x 4-5/16 in. | - | Washable or media |
No internal filter rack in this furnace - an external filter is required.
Side-return filters can differ in size - measure the existing filter.
Minimum clearances to combustibles · 59TP6A
| Position | Clearance |
|---|---|
| Rear | 0 in. (0 mm) |
| Front (combustion air openings) | 1 in. (25 mm) |
| Front, required for service | 24 in. (610 mm) - check local code |
| All sides of supply plenum | 1 in. (25 mm) - check local code |
| Sides | 0 in. (0 mm) |
| Vent | 0 in. (0 mm) |
| Top of furnace | 1 in. (25 mm) |
Keep 1 in. from combustibles to supply duct for 36 in. horizontally from the furnace.
Do not set on carpet or combustible tile; downflow on combustible floor needs the accessory floor base unless on a matching coil casing.
- Filter sizes by casing width · 58SB0A/58SB1A
Models that show this code
22 models in 59TP6A, 58SB0A/58SB1A
Other codes on the same units
- 25 Invalid model selection or setup error
- 31 High-heat pressure switch or relay did not close or reopened
- 32 Low-heat pressure switch did not close or reopened
- 34 Ignition proving failure
- 43 Low-heat pressure switch open while high-heat switch closed
- 45 Control circuitry lockout
- LED OFF No amber LED - no power to control
- Rapid Flash Reversed 115-V polarity (or twinning phasing)
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Source: Carrier 59TP6A Installation, Start-up, Operating and Service Instructions, Fig. 66 Troubleshooting Guide (cont.), p.89. Summarized in our own words; check the original manual for your model.
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For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.