Get a small pot, fill it with about a 1/2 to 3/4 inch of water... Heat the water on the stove till is just starts to boil then back the heat down.. Put ur vial in the hot water bath and keep an eye on it.. Periodically pull the vial out of the water, wipe it off with a towel and look at it.. If all the crystals re-dissolved your good... If not give the vial a swirl and put back in the bath... This should take no longer than ten minutes to complete... When you store your vials keep them out of the cold and they shouldn't crash...
You can vent it, but its not advised as it may let bacteria in.. All vials should have enough head room
(space between the top of the oil, and bottom of the stopper), to allow for enough expansion..unless it filled to the damn brim, lol...
In the home brew world, once you have filtered your gear, many people will use a pressure cooker to sterilize the filtered product.. This final step in the process requires that the gear be baked at 15psi (roughly 250*F) for at least 30min..
Water boils at 212*F, and with what your doing your not even coming close to the temp and pressure to remotely even make a crimped vial stopper bulge... Vent it at your own risk...
No offense taken. I have never had this issue since I live in a warm climate year round. I was thinking equalization of pressure in vial with atmospheric pressure would keep user from being surprised when pinning vial and not have some sort of blow back if gear is still warm.btw.. This was not meant to discredit anyone else's response... I would just hate so see someone UN-DO the great work by some of the awesome chemists out there...
Good advice
One thing I would add is put a needle inside top of vial when heating to vent air as it will expand during the heating process.