HVACopediaCarrier · Furnace
34.3 Flame lost after blower on-delay
What the control is telling you
Flame was proven after ignition but then lost after the heating blower on-delay, with the blower running.
Applies to: Carrier 59SC6A
Likely causes
- Blower airflow disturbing the flame (cabinet/heat exchanger leakage)
- Dirty flame sensor
- Gas pressure drop
- Vent issue
- Return air drawn from the furnace space
Test and repair steps
- Warning: Flame disturbed when the blower starts can point to a heat exchanger or cabinet leak; inspect carefully before returning the unit to service.
- Confirm the blower door is installed and return duct is sealed to the furnace.
- Clean the flame sensor with 0000 steel wool only.
- Check gas pressure with the blower running.
- Inspect vent and combustion-air pipes.
- Inspect heat exchanger cells; clean openings with vacuum and soft brush if burner assembly is removed.
- Run 2 complete cycles watching for flame lift or roll when the blower starts (25 s after the gas valve opens).
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
- 32.1 Main pressure switch (LPS) open
- 33.1 Main limit circuit switch open
- 34.1 Ignition fault during ignition trials
- 34.2 Flame lost before blower on-delay
- 45.1 Control failure - flame circuit / memory / sequence
- 45.2 Control failure - gas valve relay will not close
- 45.3 Control failure - EEPROM memory
- 46.1 Momentary loss of power
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
Source: Carrier 59SC6A Installation, Start-up, Operating and Service Instructions, Fig. 60 Service Label p.54; Sequence of Operation p.69; Heat exchanger cleaning p.68. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
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.