You didn't specify whether the pressure valve leaks from its drain or where it screws in the tank If it leaks where it screws into the tank I'd remove it & apply some pipe thread sealant. I always do this as a matter of routine. It takes little time & materials. Don't assume that the valve is sealed from the factory, tho it should be. Luckily the valve is at the top so you won't have to drain much water. Just remember to cut power to the heater before you drain it & wait till it fills back up to re-apply power. If the valve leaks from its drain opening then it may be defective. Should be covered under warranty. .