Unit locks out with A05; fan may run but burner does not ignite

Safety: Isolate power before removing the front cover. Do not operate the heater with the cover removed except for brief diagnostic checks by a professional.

• 1. Check flue and air intake: Ensure the concentric flue terminal is clear of obstructions. Remove any visible debris around the air intake.
• 2. Reset and listen: Reset the heater and listen for the fan. If the fan does not start, the fan motor or its power supply may be faulty.
• 3. Inspect pressure switch tubing (technician-level): Remove the front cover. Locate the air pressure switch and its silicone tubes. Check for splits, kinks, or water in the tubes. Clean or replace as needed.
• 4. Test air pressure switch: A technician can use a manometer or gently apply suction to confirm the switch changes state and that the control board detects it.
• 5. Fan inspection: Check that the fan impeller spins freely and is not obstructed by dirt or foreign objects. Replace the fan assembly if seized or noisy.