Display shows H04 and heater will not ignite; unit may click repeatedly without starting.

Danger: This fault involves the gas valve. Incorrect handling can cause gas leaks or fire. If you are not a trained gas technician, do not attempt internal gas valve repairs.

• 1. Power cycle: Turn OFF power for 5 minutes, then restore and try again. If H04 returns immediately, proceed cautiously.
• 2. Verify gas valve is open: Ensure the manual gas shutoff valve to the heater is fully open.
• 3. Inspect wiring (qualified persons):
  • Remove the front cover.
  • Locate the gas control valve assembly.
  • Check the electrical connector for secure fit and signs of heat damage.
  • Reseat the connector.
• 4. Check for incorrect gas type setting: If the heater was recently installed or converted (LPG vs. NG), verify with the installation manual that the DIP switches or PCB settings match the gas type. Incorrect settings can trigger H04.
• 5. If H04 remains: The gas valve or main PCB is likely defective and must be tested and replaced by an authorized Panasonic service technician. Do not attempt to open or adjust the gas valve body yourself.