The furnace has locked out after three unsuccessful ignition attempts. A qualified technician should diagnose why flame cannot be established or maintained.
Professional Required
Furnace lockout due to an excessive number of ignition retries (3 total)
Furnace fails to operate; LED displays E0 and ComfortNet thermostat shows ‘Check Furnace’
Failure to establish flame or loss of flame after establishment due to no gas, pressure switch stuck open, bad igniter/alignment, improper orifices, coated or improperly connected flame sensor, interrupted gas supply or lazy burner flame
A technician should check ignition, gas supply, flame sensing and relevant safety circuits. Do not repeatedly reset the furnace or work on gas components.
Gas supply, front‑cover pressure switch, igniter, flame sensor, flue piping, induced‑draft blower
Contact a qualified HVAC technician for diagnosis and repair; do not bypass safety devices or attempt internal gas or electrical repairs.
If you smell gas, leave the area and contact your gas utility or emergency services from a safe location. Never bypass safety controls. Internal furnace servicing should be performed by qualified personnel.
Learn more about the furnace components and operating conditions commonly associated with diagnostic error codes: