Boiler shows F.03 and will not fire, fan may run briefly then stop

Safety first: Disconnect power to the boiler before opening any panels. Do not bypass safety devices.

• Inspect intake and exhaust: Check the entire length of the combustion air intake and exhaust vent for obstructions, kinks, or disconnections. Clear any debris, ice, or insect nests. Ensure terminations are not blocked by vegetation or snow.
• Check pressure tubing: Locate the air pressure switch and its silicone tubes to the blower or vent connection. Inspect for cracks, splits, moisture, or dislodged ends. Re-seat any loose tubing and replace if hardened or damaged.
• Verify condensate drainage: A flooded heat exchanger or vent can affect pressure readings. Confirm the condensate trap and drain line are clear and properly sloped. Clean the trap and flush lines if needed.
• Listen to the blower: Restore power and call for heat. Listen for the combustion blower starting. If the blower does not run, or makes grinding/squealing noises, it may be failing and should be replaced by a technician.
• Reset control: After correcting obvious issues, reset the boiler and observe if F.03 clears. If the error persists, the air pressure switch or blower may need electrical testing and replacement.

Professional help: If the pressure switch is suspected faulty or the blower does not start, contact a qualified technician. Do not jumper or bypass the air pressure switch.