Power vent A.O. Smith water heater shows E04 and will not fire

Safety: Disconnect electrical power and shut off gas before working on the blower assembly.

• 1. Listen for blower: When there is a call for heat, you should hear the blower start before ignition. If it is silent, suspect a blower or control issue.
• 2. Inspect blower: Remove the blower access cover. Check for obvious damage, water intrusion, or debris in the blower wheel. Spin the wheel by hand (with power off); it should turn freely without grinding.
• 3. Electrical checks: Verify the blower wiring harness is fully seated on the blower and control board. Look for burnt connectors or melted insulation. Tighten or replace damaged connectors.
• 4. Power to blower: A technician can measure voltage at the blower terminals when the unit calls for heat. If proper voltage is present and the blower does not run, the blower motor is likely failed and must be replaced.
• 5. Control board: If the blower never receives power, the control board or gas control valve with integrated blower relay may be defective and require replacement.

Because this involves combustion air and venting safety, blower replacement should be done by a qualified technician if you are not experienced with gas appliances.