A gas appliance needs approximately one square inch of unobstructed air vent per 1K BTu of burner. Depending on the size of the louvers, you still may not have enough free air. A second thought is how tight the whole condo is, if it is well sealed, or you have other problems with the furnace, dryer, exhaust vents, you may end up with negative pressure in the house. If, for example, you have a range hood that actually vents outside, it could be pulling a slight vacuum in the house. Couple that with the dryer, adn maybe a stove, and the bathroom vents, and you could be starving the WH from enough air. It could be that those other users of air are pulling it through the flue, and this pushes the pilot away from the sensor, which then cools off and shuts things down. Lots of if's there, and probably more. You may need an air-to-air heat exchanger to bring in enough fresh air to overcome the problem.