How to Fix an Error code 6 on AO Smith GPDH 50

How to fix the power-vent AO Smith water heater (GPDH 50), with an error code 6, due to the ignition and flame problems?

There are several reasons why the AO Smith water heater GPDH 50 has ignition or flame failure problems. In such a case, the unit will try to ignite the gas burner, and if the maximum number of repeats has been reached, the system will lock out for approximately one hour. As the unit is equipped with the Intelli-Vent gas control valve, it will display the error codes 6 where two indicator lights, A and B, will be on.

To reset the heater, you must first cycle the power to the unit OFF and ON.

Note: The Intelli-Vent is the device that is in charge of the temperature, ignition, blower, and ignitor control, also flame sensing and gas regulation. It also features advanced diagnostics, and it incorporates 6 LED lights and two buttons for adjusting the temperature from warm to hot. The Intelli-Vent control uses the silicon nitride ignitor, which is more durable than the ignitors found on most water heaters.

Back to the problem…

The main cause of ignition failure is a broken or malfunctioning ignitor. The first thing that needs to be checked is the resistance of the element. The resistance should be between 11.5 and 18.8 ohms and must be replaced if it is not. Keep in mind that the element resistance changes over time.

Other causes of the ignition/flame failure:

• Low pressure – the manifold gas pressure cannot be adjusted, so if it is off by 0.3” W.C., you must replace the gas control valve. Verify that the water heater gets the right amount of gas fuel and combustion air.
• Low voltage – the voltage must be between 115 and 125 VAC. 
• Poor contact – ensure the correct contact between the flame sensor and flame (required gap – 0.13” and elevation 0.4” – measured from the lower lip on low NOx and from the top lip on standard burners).
• Make sure the flame sensor is always clean – use the fine steel wool to clean from any residues.
• Ensure there are no cracks or damages to the flame sensor and its insulation.
• Ensure the right vent size and lengths are used.
• Dislodged or missing flue restrictor or baffle can cause excessive air turbulence.
• Vent termination restrictor is installed only if required.