34.1 Ignition fault during ignition trials

What the control is telling you

Flame was not proven during the four consecutive ignition trials.

Applies to: Carrier 59SC6A

Likely causes

• Low gas pressure or gas off
• Weak/failed igniter
• Dirty flame sensor
• Gas valve not opening
• Poor ground

Test and repair steps

1. Warning: If you smell gas, shut off the gas and fix the leak before any ignition attempt.
2. Know the sequence inducer starts, LPS closes, 15-s prepurge, 17-s igniter warm-up, gas valve opens, then a 2-s flame-proving window starts 5 s after the valve opens. Failure to prove flame repeats for up to 3 more trials (4 total), then lockout.
3. Confirm the manual gas shutoff is open and natural gas supply pressure is 4.5-14 in. w.c.
4. Watch a trial does the HSI glow? Check HSI cold resistance across both leads at room temperature: 40-70 ohms. Replace if out of range or damaged.
5. Does the gas valve open (24 VAC at valve) and burners light? If no gas with 24 VAC present, suspect the valve; check manifold pressure (2.8-3.8 in. w.c. natural gas for 40k-120k models; max 1.8 in. w.c. on 26k model).
6. If burners light then go out within ~2 s, clean the flame sensor with 0000 steel wool only (no sandpaper or emery cloth) and check its position.
7. Verify ground the control proves flame through the green/yellow ground to the gas valve and manifold bracket; the flame-sense ground wire must be attached to furnace sheet metal.
8. Check igniter alignment and orifices for blockage.
9. The control retries automatically; four failed trials in a row gives 14.1 lockout.

Settings for these units

• Filter sizes by casing width and filter cabinet · 59SC6A
• Minimum clearances to combustibles · 59SC6A