Furnace will not ignite; inducer runs but burners never light; status LED shows 3 flashes repeating.

Safety: Turn off power before removing furnace doors. Working on venting at height or outdoors may require fall protection and weather precautions.

Diagnostic steps:

• Check vent system: Inspect the exhaust and intake (if applicable) PVC pipes from the Concord furnace to the outside. Remove any visible obstructions such as leaves, bird nests, or ice. Ensure terminations are not buried in snow.
• Inspect inducer motor: With the access panel removed, call for heat and observe the inducer. It should start promptly and run at full speed. Listen for grinding or humming. If the inducer fails to start or is very weak, it may not create enough draft to close the pressure switch.
• Examine pressure tubing: Remove the rubber hose from the pressure switch and inducer port. Check for splits, kinks, or soft spots. Replace tubing if deteriorated. Ensure the port on the inducer housing is not plugged with rust or debris; clean gently with a small drill bit or wire (do not enlarge the hole).
• Test pressure switch: With a multimeter, check continuity across the pressure switch terminals. When the inducer is off, the switch should be open (no continuity). When the inducer is running, the switch should close (continuity). If it never closes even with good draft, replace the pressure switch.
• Reset and test: After clearing any blockages and verifying components, restore power and test a full heat cycle.

Call a technician if: The venting is complex, runs through walls/roof, or you suspect undersized or improperly sloped venting. Improper venting can cause carbon monoxide hazards.