Boiler shows E3 and will not start; fan may run briefly then stop

Safety first: Turn off power. Do not operate the boiler with venting disconnected. Carbon monoxide hazard.

Steps:

• Inspect vent and intake: For Peerless direct-vent boilers, check the PVC or polypropylene intake and exhaust terminations outside. Remove snow, ice, leaves, or insect nests.
• Check condensate drain: A clogged condensate trap or hose can flood the combustion chamber and affect the pressure switch. Clean the trap and ensure hoses are clear and sloped properly.
• Inspect pressure switch tubing: Remove the front panel and locate the air pressure switch. Verify the silicone tubing is firmly attached and not cracked or kinked. Replace if brittle.
• Test pressure switch: With power off, gently blow through the tubing to ensure it is clear. A technician can test continuity across the switch while the inducer runs.
• Check inducer fan: Spin the inducer wheel by hand; it should move freely. Listen for grinding or seized bearings.
• If E3 remains: Have a professional replace the air pressure switch or inducer assembly and verify combustion safety.