Lennox Furnace Error Codes
Lennox furnaces range from value ML-series units to premium communicating SLP98 systems. Legacy models flash an LED fault code; communicating iComfort systems show a numbered alert on the thermostat. Either way, the fault conditions below cover the vast majority of Lennox no-heat calls in BC.
How Lennox shows faults: Legacy Lennox furnaces flash an LED code on the control board; iComfort communicating systems display a numbered alert on the thermostat. The conditions below explain what they mean.
Ignition Lockout
highYour Lennox furnace failed to establish flame across its trials and locked out. Communicating models (iComfort) show a numbered code on the thermostat; legacy boards flash an LED code.
Weak Flame Signal
highThe flame-sensing current is too low and the board drops the gas valve to stay safe — common as the sensor ages on SLP98/EL296 and similar models.
Pressure Switch Stuck Open
highThe inducer ran but draft was never confirmed, so the Lennox control blocks ignition.
Open High-Limit Switch
highThe high-limit opened on excess temperature — an airflow fault that shortens heat-exchanger life if left unaddressed.
Flame Rollout Switch Tripped
criticalFlame rolled out of the burner box and tripped the rollout safety. Safety-critical and a possible sign of a cracked heat exchanger — requires technician diagnosis.
iComfort Communication Fault
moderateOn communicating Lennox systems, the furnace, thermostat and outdoor unit talk over a data bus; a communication fault disables staging or the whole system.
Blower or Inducer Motor Fault
highThe Lennox control cannot run the inducer or variable-speed blower as commanded and shuts down.
Need a Lennox technician in Greater Vancouver?
Furnace and heat-pump service is handled by our parent company, CANRO Heating & Cooling — same-day & after-hours. Call 604-359-1081.
Lennox furnace acting up?
CANRO Heating & Cooling — same-day diagnosis across Greater Vancouver. Call 604-359-1081.