Boiler displays F.13, often during very cold weather or long vent runs

Safety first: Turn off power before inspecting intake piping.

• Check outdoor intake terminal: Clear any snow, ice, leaves, or debris from the combustion air intake. Ensure the screen is clean.
• Inspect intake piping: Follow the intake pipe from the boiler to the outside. Look for crushed sections, disconnected joints, or foreign objects.
• Verify slope and support: Ensure the intake is properly supported and not sagging, which can collect condensate.
• Reset and test: After clearing obstructions, restore power and reset the boiler. Observe if F.13 returns.

Professional help: If the intake system appears clear but the fault persists, a technician should verify blower performance and pressure readings.