13.1 Limit lockout - main limit open over 3 minutes

What the control is telling you

A switch in the main limit circuit stayed open for longer than 3 minutes, so the control locked out heating.

Applies to: Carrier 59SC6A

Likely causes

• Dirty or restricted filter
• Closed supply/return registers or undersized ductwork
• Heating airflow setting too low / high temperature rise
• Blower motor problem
• Over-firing (gas pressure or orifice wrong)
• Manual-reset flame rollout switch open

Test and repair steps

1. Warning: Never jumper the limit or flame rollout switches.
2. Check and clean/replace the filter (it is external to the casing); open all registers and check ducts for restrictions.
3. Measure temperature rise with the blower door on: duct thermometers in supply and return near the furnace, out of line-of-sight of the heat exchanger. It must be within the rating-plate range; midpoint or slightly above is recommended.
4. If the rise is high, check gas input rate, altitude derate, and duct static; static above 0.50 in. w.c. is excessive.
5. Raise the Ht heating airflow setting to lower the rise (lower it to raise the rise).
6. Check manifold pressure for 40,000-120,000 BTUh models it must be 2.8-3.8 in. w.c. on natural gas; on the 26,000 BTUh model (green label on gas valve solenoid, Table 26) do not exceed 1.8 in. w.c.
7. Check blower operation with the Ct component test; check the blower wheel and motor are clean.
8. If a manual-reset flame rollout switch tripped, correct combustion air, gas pressure, burner/orifice position or venting before resetting it.
9. Verify the limit works run the furnace at least 5 minutes, slowly block the return air until the limit trips, then unblock; burners should relight once it cools.

Settings for these units

Filter sizes by casing width and filter cabinet · 59SC6A

Side-return filters can differ in size - measure the existing filter.

Every return-air inlet needs a filter.

Minimum clearances to combustibles · 59SC6A

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

• 10.1 L1 polarity fault
• 12.1 W (heat call) on at power up
• 14.1 Ignition lockout after 4 tries
• 14.2 Lockout - flame lost 3 times after 70 s of heating
• 14.3 Lockout - 7 flame-loss events in one heat call
• 21.1 24 VAC on gas valve when it should be off
• 22.1 False flame
• 23.1 Main pressure switch stuck closed