Furnace LED shows code 31 (pressure, draft safeguard, or auxiliary limit switch open). Inducer may run but burners do not light.

Safety first: Turn off power and gas. Working on venting and combustion air systems can affect safety.

• Check vent termination: Go outside and inspect the furnace exhaust and intake (if present). Remove any ice, snow, leaves, or nests blocking the PVC or metal vent pipes.
• Inspect inducer motor: Remove the burner compartment door and locate the inducer assembly. With power on and a call for heat, verify the inducer starts and runs smoothly without loud grinding. If it hums but does not spin, it may be seized.
• Check pressure switch tubing and ports: Remove the tubing from the inducer and pressure switch. Clear any debris or water. Use a small drill bit by hand or a paper clip to gently clean the inducer port (do not enlarge the hole).
• Condensate drain (high-efficiency models): Inspect the condensate trap and hoses. Clean the trap and ensure hoses are not kinked or blocked. A full trap can cause pressure switch faults.

If the code 31 persists after these checks, the pressure switch, auxiliary limit, or inducer assembly may need professional testing and replacement.