I make it a habit of putting my primer/paint spray Can in hot water but in teh past couple of day I have found that two of teh cans do not spay anymore. I press down on teh nozzle but nothing coming out. Nay suggestions as to why this might be happening and any remedies

Sounds like theres paint dried in the nozzle (the white piece on top of the can)
This will come off easily and then place it in some thinners overnight. If your using acrylic primer isopropyl will be fine, if its enamel then use white spirit.
This is assuming of course,,that you havent got an empty spray can
Nige

As Nigel sayes it's probably a clogged nozzle. I get that quite often I clean them or use a nozzle from another can.
Next time you use a can, after you've finished painting, try turning the can upside down, and spray for a few seconds. This will blow some of the paint out of the nozzle.