4 Limit or rollout circuit open

What the control is telling you

The main limit or flame rollout switch is open. The blower runs at least 4 minutes or until the switch closes. If open longer than 3 minutes the code becomes 7. The rollout switch must be reset by hand.

Applies to: KeepRite (F/G)9MXE single-stage and (F/G)9MXT two-stage 95% furnaces

Likely causes

• Dirty filter or restricted ductwork
• Loose blower wheel
• Gas input set too high
• Wrong limit switch or missing limit gasket
• Faulty switch or wiring

Test and repair steps

1. Replace or clean the filter and check that supply/return registers are open.
2. Check the blower wheel is tight on the shaft and turning at speed.
3. Clock the gas meter and correct the manifold pressure if the furnace is overfired.
4. Check the limit is the correct part and its gasket is in place.
5. If the rollout switch tripped, find out why (combustion air, venting, burner alignment) before pressing reset.
6. Check switch continuity and wiring.

Settings for these units

• Filter size by casing width · KeepRite (F/G)96VTN Two-Stage Variable-Speed Furnace

Models that show this code

16 models in KeepRite (F/G)9MXE Single-Stage Furnace, KeepRite (F/G)9MXT Two-Stage Furnace

Other codes on the same units

• 1+2 Blower running after power-up (normal)
• 2 Pressure switch stuck closed (did not open)
• 3 Pressure switch did not close or reopened
• 5 Flame sensed with gas valve off
• 6 Flame not proved during ignition trial
• 6+1 Ignition lockout after 4 failed tries
• 7 Limit circuit lockout
• 8 Gas heating lockout - manual reset needed