Lennox Furnace Error Code 5+1

The 5+1 flash code on a Lennox furnace indicates a hard lockout caused by an open rollout circuit. The rollout switch, a thermal safety device near the burners, has detected flame rollout and tripped, cutting power to the gas valve and ignition system. This is a hard lockout, meaning the furnace will not attempt to restart until the switch is manually reset and power is recycled to the control board. The underlying cause of the rollout condition should be investigated before returning the furnace to regular service.

Yes, a rollout condition is a genuine safety issue. Flame rollout means combustion flames are escaping the burner box into areas of the furnace not designed to handle that heat, which can damage wiring, components, and in severe cases pose a fire risk. The rollout switch exists specifically to shut the system down when this occurs. Do not simply reset the furnace and ignore the code without investigating why the rollout happened.

Repair costs vary widely depending on the cause. If a technician only needs to clean the burners and clear a blocked flue, service call and labor costs typically range from $80 to $200. Replacing a faulty rollout switch is a relatively inexpensive part repair, generally in the $100 to $250 range including labor. However, if a cracked heat exchanger is causing the rollout condition, replacement costs can range from $500 to well over $1,500 depending on the unit and labor involved.

Start by locating the rollout switch on the burner assembly and pressing its manual reset button. Next, inspect all wiring connections to the switch for loose terminals or damage, then cycle power to the furnace off and back on to clear the hard lockout on the control board. If the furnace fires successfully but the rollout switch trips again, a technician needs to inspect the flue venting, burner assembly, and heat exchanger to identify the root cause.

Cycling power to the furnace will clear the hard lockout state stored in the control board, but the rollout switch itself must also be manually reset by pressing its button before the furnace can fire. If the root cause of the rollout, such as a blocked flue or dirty burners, is not corrected, the switch will trip again and the 5+1 code will return. Resetting without addressing the underlying problem is a temporary measure at best.