How to Fix an Error Code 6 on AO Smith GPDH 50 Water Heater

When error code 6 surfaces on your AO Smith GPDH 50 power-vent water heater, signaling ignition and flame-related issues, it's essential to take immediate action.

To help you navigate and resolve this problem, follow the steps found in this guide.

Understanding AO Smith GPDH 50 water heater

The AO Smith GPDH 50 is a gas-powered, power-vented water heater with a 50-gallon tank capacity. It is ideal for households with moderate to high hot water demands, ensuring an abundant supply for showers, baths, laundry, and other daily needs.

This water heater utilizes a blower fan to efficiently expel combustion gases, providing flexibility in installation and significantly enhancing energy efficiency when compared to traditional atmospheric vent models.

Understanding Intelli-Vent gas control valve

One standout feature of this water heater is its Intelli-Vent gas control valve. This advanced valve ensures precise control over gas flow, ignition, and flame sensing, guaranteeing a safe and reliable operation.

Additionally, the Intelli-Vent control utilizes a silicon nitride ignitor, renowned for its durability when compared to standard water heater ignitors.

Moreover, it boasts advanced diagnostic capabilities, featuring six LED lights and two temperature adjustment buttons, providing a range from warm to hot for enhanced user control and convenience.

Error code 6 explained

Error code 6 is a specific error message displayed by appliances equipped with the Intelli-Vent gas control valve, including AO Smith water heaters like the GPDH 50. This error code typically indicates a problem related to ignition and flame issues within the appliance.

Usually, the unit will attempt to ignite the gas burner. However, if the maximum number of ignition attempts is reached, the system will enter a lockout state for approximately one hour.

To potentially resolve the issue, consider resetting the water heater. You can start by power-cycling the unit, turning it OFF and then back ON. This initial troubleshooting step may help rectify the problem.

Identifying key causes of ignition and flame failure, and solutions

  • Faulty or broken ignitor: The initial step is to check the resistance of the ignitor element, which should fall within the range of 11.5 to 18.8 ohms. If it falls outside this range, you should replace the ignitor. Keep in mind that the element's resistance can change over time.
  • Low gas pressure: Ensure that the manifold gas pressure is within the specified range. If it deviates by 0.3” W.C., you may need to replace the gas control valve. Verify that the water heater receives the correct amount of gas fuel and combustion air.
  • Low voltage: Make sure the voltage remains within the range of 115 to 125 VAC.
  • Poor contact: Confirm that there is proper contact between the flame sensor and the flame. The required gap should be 0.13”, and the elevation should be 0.4”, measured from the lower lip on low NOx burners and from the top lip on standard burners.
  • Maintain cleanliness: Ensure that the flame sensor is consistently clean by using fine steel wool to remove any residues.
  • Inspect for damage: Examine the flame sensor for cracks or damage, and inspect its insulation for potential issues.
  • Ventilation and flue: Confirm the correct vent size and lengths are in use, and ensure there are no dislodged or missing flue restrictors or baffles that may cause excessive air turbulence.
  • Restrictor installation: Only install a vent termination restrictor if it's deemed necessary.


Understanding and addressing error code 6 on your AO Smith GPDH 50 power-vent water heater, associated with ignition and flame issues, is vital to ensure the consistent and safe operation of your appliance.

By following the outlined troubleshooting steps and considering the potential causes discussed, you can diagnose and resolve the problem effectively.

Regular maintenance and attention to the various components, such as the ignitor, gas pressure, voltage, flame sensor, and ventilation system, are essential for maintaining the efficiency and longevity of your water heater.

If you encounter challenges or uncertainties during this process, seeking professional assistance is always a wise choice to ensure your water heater continues to provide reliable hot water for your household's needs.

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