Boiler locks out with E03; fan may not start or stops quickly; no ignition attempt.

Safety: Turn off power before removing the front cover. Do not operate the boiler with the cover removed except for brief testing by a professional.

• Inspect venting: Go outside and check the IBC boiler intake and exhaust terminations. Remove any snow, leaves, insect nests, or debris. Ensure vent screens are clear.
• Check intake air path: Inside, inspect the intake pipe connection to the boiler. Make sure it is not crushed, disconnected, or blocked.
• Listen for fan operation: Restore power and call for heat. Listen for the combustion fan starting. If it is silent or makes grinding noises, the fan assembly may be seized or failing.
• Check wiring: With power off, verify the plug to the combustion fan motor and any air pressure switch/sensor connectors are fully seated and free of corrosion.

If E03 persists after clearing vents and checking connections, the combustion fan or air proving device should be tested and replaced by a qualified technician, as incorrect operation can lead to unsafe combustion.