I don't usually have the jars all that hot, if they are clean and dry I put them in the oven to warm them then pour in the hot jam till about 1/2 inch from top then I put the lid on and screw on very tightly. Tip the jar upside down on a wooden board or newspaper leave about 1/2 hour then I turn them up the right way. Usually you will then hear the lids make a little noise as the centre is sucked down. (They don't do this straight away) Leave until cold. To see if they are sealed, press in the centre if the lid does not go down it has sealed (you will be able to feel that it is indented) if the centre moves up and down it has not sealed. Like Jamberie I would use that one first. Hope that makes senseMarie