AO Smith water heater about 4 years old pilot went out took out piolt assembly cleaned and was able to relight pilot unit stayed working for about 2 weeks and went out again any ideas?

I had the same thing happen to me. It ended being the control. The control coil was faulty. The heater was only two years old. I tried the same things that you have.

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.

1) Reliance is AO Smith-American, and air intake screen located on bottom of water heater. Clean air intake. Replace thermocouple. First two digits of serial number are year of manufacture.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
http://waterheatertimer.org/How-to-replace-thermocouple.html

2) Add comment and say what you tried so far.
Include age of water heater.

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

Copy following link for troubleshoot by type of gas control valve
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
Use mirror to inspect arrestor screen.
http://waterheatertimer.org/images/Flame-trap-inspection-325.jpg

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

In my first 15 years as a plumber I never saw a pilot light issue on a gas WH that a new thermocouple didn't fix. Since the government mandated a redesign of the fire box, I've seen three that nothing ever fixed - two Whirlpools and one (my usually ultrareliable) AO Smith - including replacing the entire burner assembly and the regulator. And I've heard of many others.

Check the thermocouple connection for tight. (Don't strip.. threaded soft metals.)
Check the microvents on the bottom ? of the burn box for dust, even if it is new.
Call Reliant and demand new units until you get one that works.
Try another model. Consider a 52gal electric.

I've always recommended gas over electric, and AO Smith and Rheem were my recommendations (and "Reliants" were "lumber yard" water heaters. Sorry.)

Since the mandated redesigns, I don't really have a "proven reliable" model to suggest. I increasingly believe the restricted air flow design is the ultimate culprit, including any changes to the thermocouple/regulator construct to accommodate the restricted air flow design. Just my hunch.

Offered for what its worth. -- plumber in Indiana.

Check to make sure the flame of the pilot is hitting the thermocoupling. If not then you can use compressed air to clean the pilot port and relight and check again. If the flame is hitting the thermocouple, then it may need to be replaced.

The Cold air screen on the bottom of the water heater is partially plugged. That is if the pilot light can be lit and stay on, but goes out when the heater should be functioning normally. This is not the removable plastic screen but a round white-yellow grid with 1/32" holes. You can try to clean it through the bottom but you may have to remove the gas line from the controller to the burner, pilot gas line, and thermocouple connection to remove that complete assembly to get access to the screen. The AO Smith booklet warns of this but they pretend the plastic screen will keep this second screen clean but it won't. After three years it was two thirds plugged.

YOUR WATER HEATER HAS WHAT IS CALLED A STANDING PILOT-STAYS LIT ALWAYS WHEN THE PILOT GOES OUT YOU LOOSE EVERYTHING. YOU HAVE TO REPLACE THE THERMOCOUPLE WHICH KEEP THE PILOT LIT. ONCE THE PILOT IS LIT THE THERMOCOUPLE SENDS IN MILLIVOLTS TO THE BURNER TO SAY ITS READY FOR BURNING
IF YOU ARE NOT FAMILURE WITH THIS REPLACEMENT PLEASE FIND SOME ONE WHO CAN. IT IS NOT HARD TO DO ASK A NABOR OR FRIENDS SOME HAS TO KNOW HOW. SERVICE COMPANYS ARE OUT FOR THE MONEY FOR A 10 MINUTE JOB

I bet your thermo couple is bad or your ports are clogged? How old is the unit?