John Wood power vent water heater shows E004 and will not start; blower does not run

Safety: Disconnect electrical power at the breaker and close the gas shutoff valve before servicing the blower.

• 1. Check power supply: Confirm the outlet or circuit feeding the heater has power using a plug-in tester or multimeter. Reset any tripped breaker.
• 2. Inspect wiring: Remove the access cover to the control area. Check the blower wiring harness for loose plugs, burnt connectors, or damaged insulation. Reseat all connectors firmly.
• 3. Test blower motor: With power disconnected, unplug the blower and measure motor winding resistance according to the service manual. An open circuit indicates a failed motor. Also spin the blower wheel by hand; it should turn freely without grinding.
• 4. Check control fuse: Some John Wood electronic controls include an inline or board-mounted fuse for the blower circuit. Inspect and replace with the exact same rating if blown. If it blows again immediately, suspect a shorted blower or wiring.
• 5. Control board output: If the blower tests good but never receives power when a call for heat is present, the control board may be defective and require replacement.

Note: Replacement of the blower assembly and control board should follow John Wood specifications to maintain safe venting performance.