Water heater locks out with E03; fan may start but burner does not ignite, or unit stops shortly after start.

Safety: Isolate electrical power. Do not operate the heater with the flue system disassembled.

• Inspect flue and air intake: Check the Weishaupt concentric flue system from the appliance to the terminal. Look for crushed pipes, disconnections, or obstructions. Clear any debris at the terminal.
• Check condensate in tubing: Locate the air pressure switch and its silicone tubes. Remove the tubes and check for water or condensate accumulation. Blow them through gently and refit, ensuring no kinks.
• Test pressure switch operation: With power restored, call for hot water and listen for the click of the air pressure switch when the fan starts. If there is no click and tubing is clear, the switch may be defective.
• Fan inspection: With power off, spin the fan impeller by hand to ensure it turns freely. Check the fan connector and wiring harness to the control board.
• Service recommendation: Replacement of the air pressure switch or fan on a Weishaupt water heater should be done by a qualified technician to ensure correct calibration.