I have a AO Smith GPVH 50 100 with an LED status code of XOXOOX. I replaced the burner assembly today and the problem still exist. Any suggestions or a possible resolve would be greatly appreciated!

You only need the thermocouple replacing. It is the safety valve that won't let the main burner light unless the pilot is fully lit. As it is gas, you should have a gas certified technician replace it.

Here you are Dorothy

AO Smith code 991 Solution for error code 991
Check the gas type of the water heater. Inspect the environment around the water heater. ... Check if there is grease and/or dirt in the burner (Part #101) and the fan motor (Part #103), especially if the water heater has been installed in a contaminated area.

Error code '991' for type ATI-110C-N by AO Smith. Cause and ...

More help here, but you probably need a service call, especially if it is a gas water heater.

https://www.google.com/search?q=error+code+of+991

..

6 flashes is typically found with power vented and flue damper type heaters ... whirlpool never sold a power vent, but they did sell the AO Smith brand flue damper series heater.
The following manual suggest the problem is either gas supply or pilot assembly.
http://waterheatertimer.org/pdf/Power-damper-troubleshoot-parts-manual.pdf

More resources on following link:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#honeywell

Maybe this error code chart for AO Smith Power vent will help you figure it out. Also link to AO Smith website. Good luck. J

https://www.hotwater.com/support/gpvh-50

Low gas pressure, dirty combustion parts, bad gas control valve.
Following link has power vent troubleshoot:
http://waterheatertimer.org/power-vent-water-heater-troubleshoot.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You need to change the elements out

There may be a draft blowing out the pilot. Place some fiberglass insulation inside the cover for the burner or pull down the insulation from inside the jacket just over the burner opening.

AO smith manuals
http://www.hotwater.com/lit/im/r-gas.html

GPVH series manual
http://www.hotwater.com/lit/im/res_gas/315465-000.pdf
You can search the manual for FV

The FV sensor shorted because it detected flammable gas

Quote manual:
Flammable liquids (such as
gasoline, solvents, propane (LP or butane, etc.) and other substances
(such as adhesives, etc.) emit flammable vapors which can be ignited
by a gas water heater's hot surface igniter or main burner. The
resulting flashback and fire can cause death or serious burns to anyone
in the area. This water is equipped with a FV sensor for detecting the
presence of flammable vapors, see Figure 3. When the sensor detects
those vapors, the unit will shut down and not operate. Should this
happen, please refer to the troubleshooting guide on pages 28-30.

Troubleshoot step 14-15 says
replace the FV sensor
call tech assistance number that shows on water heater
AO Smith will refer you to a plumber
I don't believe homeowner can buy these parts due to Federal regulations
The shorted FV sensor probably saved you a flash-over
The cost of 2nd degree burns from a flash-over would be astronomical.
Fortunately you're ok, and the other folk in the room are ok.
In the old days.
Two guys I knew, winter 1978 Chicago, were laying VA tile using the black mastic.
They were killed and the house burned down because of the water heater.
Main office marked the event with a memo saying they still owed money on their account.

The only company with a re-settable FVIR that I'm aware right now is Bradford White
http://www.thetankatwaterheaterrescue.com/forums/forum3/2679.html
http://411plumb.com/bradford-white-defender-water-heater-review
Bradford White Defender FVIR is resettable without buying parts.

This system uses an electrical test to make sure that the burner is lit. The flame sensor will either be broken or will be covered in deposits (clean with an emery cloth).

The flame sensor is usually a small metal rod that would be in the direct line of fire of the burner with 1 wire attached.

CAUTION:

The ignitors can be very fragile and are expensive. They are very brittle, do not touch it.

Unless your AO is a high recover it will take a while for it to fill up with the water that you have used then reheat the water in the tank.