Unit displays E003 and shuts down; blower may run briefly but burner does not light.

Safety: Disconnect power before opening the cabinet. Do not operate the heater with venting disconnected except as a brief diagnostic step in a safe, ventilated area per manufacturer guidelines.

Diagnostic steps:

• 1. Inspect venting: Check the PVC intake and exhaust pipes for obstructions such as leaves, nests, ice, or snow. Clear any blockage and ensure terminations meet Lochinvar clearance requirements.
• 2. Check condensate drain: A backed-up condensate trap can flood the combustion chamber and affect pressure readings. Verify the condensate trap and drain line are clear and properly sloped.
• 3. Examine pressure switch tubing: Locate the silicone tubing between the combustion blower and the air pressure switch. Ensure it is not cracked, kinked, or disconnected. Replace if brittle or damaged.
• 4. Test the pressure switch: With power off, disconnect the wires and check continuity across the pressure switch terminals while gently applying suction to the tubing port. The switch should close (show continuity) when suction is applied. If it does not, replace the pressure switch with the correct Lochinvar part.
• 5. Verify blower operation: Restore power and observe whether the combustion blower starts when a call for heat occurs. If the blower does not run or is noisy and slow, it may be failing and require replacement.
• 6. If E003 persists: After clearing vents and verifying the switch, further diagnosis of the control board and blower speed may be needed by a qualified technician.