Furnace frequently goes into lockout during very cold weather, with no specific code or intermittent codes.

Safety: Take care when working outside in icy conditions.

• Check condensate outlet: Inspect the external condensate pipe for ice. Thaw gently with warm water and insulate the pipe afterward.
• Inspect flue terminal: Remove any ice buildup around the flue terminal without damaging it.
• Improve fall and size (professional): A technician can reroute or upsize the condensate pipe to reduce freezing risk.
• Reset furnace: After clearing ice, reset the furnace and monitor operation.