HVACopediaCarrier · Furnace
14.2 Lockout - flame lost 3 times after 70 s of heating
What the control is telling you
Flame was established but lost 3 times after 70 seconds of heating, so the control locked out.
Applies to: Carrier 59SC6A
Likely causes
- Dirty or weak flame sensor signal
- Low or fluctuating gas pressure
- Poor ground
- Flue/combustion air problems disturbing the flame
- Pressure switch opening during the cycle
Test and repair steps
- Warning: Turn off gas and power and lock out before removing burner parts.
- Clean the flame sensor with 0000 steel wool only (no sandpaper or emery cloth); check it sits in the flame.
- Verify ground continuity green/yellow wire to gas valve and manifold bracket screw, and the flame-sense ground wire to furnace sheet metal.
- Check natural gas supply (4.5-14 in. w.c.) while burning and manifold pressure (2.8-3.8 in. w.c. for 40k-120k models; max 1.8 in. w.c. on 26k).
- Inspect burners and orifices for dirt or blockage; clean burner with brush and vacuum.
- Inspect vent and combustion-air pipes for water, sags or blockage.
- Run 2 complete heat cycles and look at the flame: it should be clear blue, almost transparent.
- Reset the lockout by briefly removing 115 VAC power, or by breaking 24 VAC at SEC1/SEC2 on the control (not at W, G or R); otherwise it auto-resets after 3 hours.
Settings for these units
Filter sizes by casing width and filter cabinet · 59SC6A
| 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 | (1) 16 x 25 x 3/4 in. | (1) 16 x 25 x 3/4 in. | Washable |
| Furnace casing | 21 in. wide | (1) 16 x 25 x 3/4 in. | (1) 20 x 25 x 3/4 in. | Washable |
| Furnace casing | 24-1/2 in. wide | (1) 16 x 25 x 3/4 in. | (1) 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 |
Side-return filters can differ in size - measure the existing filter.
Every return-air inlet needs a filter.
Minimum clearances to combustibles · 59SC6A
| Position | Minimum clearance |
|---|---|
| Rear | 0 |
| Front (combustion air openings in furnace and in structure) | 1 in. (25 mm) |
| Required for service | 24 in. (610 mm) (see note) |
| All sides of supply plenum | 1 in. (25 mm) (see note) |
| Sides | 0 |
| Vent | 0 |
| Top of furnace | 1 in. (25 mm) |
Service and supply-plenum values are marked 'consult local building codes'.
Keep 1 in. (25 mm) from combustibles to supply ductwork for 36 in. (914 mm) horizontally from the furnace.
Models that show this code
11 models in 59SC6A
Other codes on the same units
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Source: Carrier 59SC6A Installation, Start-up, Operating and Service Instructions, Fig. 60 Service Label p.54; Cleaning Burners and Flame Sensor p.66; Fig. 61 notes p.56. 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.