I have a Rheem PowerVent 2 75 galoon lp gas heater model number 22VRP75P. The vent fan comes on, pilot clicks and ignites, burner does not. After three tries, the unit powers down, LED light flashes twice. After shutting it off at the fan, I have been able eto get it to restart. Is this a an ignition control module problem? If so, what is the part number.

There is no pilot light on your power vented hot water heater. You may as well unplug it because the induction fan will continue to run. Hopefully your propane company is responsible enough to perform a gas leak check on your propane system. After the gas is turned back on, you can plug in your water heater to start it up. Run-outs are costly so it's bet to get on automatic delivery or call when the tank is down to 30%

`1) Copy following link to troubleshoot by type of gas control valve, blower motor links, pressure switch testing, and other professional resources:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
http://www.thetankatwaterheaterrescue.com/forums/forum3/

2) Power-vent blower motor can go bad.
Plug motor directly into outlet, or turn on-off switch on, and see if motor works.
Check outlet for correct polarity, and for at least 80% of rated voltage.
Check vacuum switch. Blower creates vacuum, and the vacuum switch detect vacuum, and signals gas control valve that burner sequence can continue.
Gas control valve can also go bad. Wiring etc can go bad.

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

Start-point is to inspect and clean burner parts and combustion chamber, clean air intake, bleed air out of gas line, test gas pressure, test electronic gas control valve, check for venting issues.
As general rule, gas water heater manuals recommend professional service once a year that would cover most items listed above.
To see images, and for more reading and resources, look at your product manual and open following link:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#clean

Richmond/Rheem sells power vent blower assembly that cost about $300.
Your product manual shows part numbers.
http://www.monstermarketplace.com/heating-supplies/rheem-sp12562-blower-assembly-powervent-2
Replacement gas control valve costs $300

CHECK THE POWER VENT UNIT

YOU MUST FOLLOW THE MANUFACTURERS CONVERSION INSTRUCTIONS EXACTLY. If you do not your homeowners policy COULD be declaired void in the event of a claim. More importantly (IMHO) you could create a dangerous situation!

It sounds like your gas/air mixture needs to be adjusted. The flame should have just the slightest amount of white, at the very tip. The rest should be evenly blue. There is an air vent adjustment in the line to the burner, right after the gas input.

Sounds like a bad thermocouple. This part sends a millivolt signal to keep the gas valve open but shuts it off when it cools - or if something goes wrong with the ignighter - to prevent fires. It's easy to replace and not super expensive. See your local Rheem dealer.

I would check to see if the switch on the blower pressure sensor is closing...When T-stat calls for flame, the circuit starts the blower, then the blower pressure sensor switch closes to allow the main gas valve to be powered.

1) common problem for this heater. Likely the pilot is igniting but the gas valve is not getting the signal back saying pilot is lit so open the main valve to burners. Easy fix with new pilot assembly. Good technician can diagnose this and change part in under 20 minutes.
To diagnose yourself go out after dark (to make pilot easier to see), turn on heater to make it spark. After it sparks 15-20 seconds pilot should be lit. With an inspection/cosmetic mirror you will either see the pilot sparking or lit. It will be in bottom right if burner cabinet, just follow the small silver tubing.
2) Second scenario, Pilot is not getting fuel. Could be clogged pilot assembly, stuck/faulty gas valve, supply line shut off valve not open.
In the event heater is in older, rusty/corroded condition there is the remote possibly of a hole in pilot tubing so gas isn't getting to the right location, just dumping into heater. If this is the case do not loose your eyebrows looking for pilot in scenario one, call a pro.