13 Limit circuit lockout

What the control is telling you

Lockout because the limit or flame rollout switch stayed open more than 3 minutes, or there were 10 successive limit trips in high heat. Auto-resets after 3 hours.

Applies to: 59TP6A two-stage variable-speed ECM multipoise condensing gas furnace, all sizes (040-10 to 120-22)

Likely causes

• Dirty filter or restricted ductwork
• Loose blower wheel
• Wrong low- or high-heat gas input
• Wrong limit switch or missing limit gasket
• Open flame rollout switch (manual reset)
• Defective switch or connections

Test and repair steps

1. 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.
2. Work through the code 33 checks; 13 is the lockout version of 33.
3. Check and replace dirty filters; inspect ducts for restrictions (static above 0.5 in. W.C. is excessive).
4. Check the blower wheel is tight on the shaft.
5. Check manifold pressure in low and high heat against Table 21 (typical 3.4 in. W.C. high / 1.4 in. W.C. low).
6. Check the flame rollout switch; it needs manual reset. Before resetting, correct combustion-air, gas pressure, burner/orifice or vent problems.
7. Confirm the correct limit switch and gasket are installed and the wiring is sound.
8. Reset by cycling 115 V power and verify temperature rise is within the rating-plate range.

Settings for these units

• Filter sizes by casing width and filter cabinet · 59TP6A
• Minimum clearances to combustibles · 59TP6A