"If I don't find any nicks or whatnot on the jar lid, why would I need to change the jar? And I thought I would definitely want to add a new lid- I don't know how I would tell if it were necessary."

The new jar recommendation is based on the assumption that you may not be able to see or feels very small nicks in the rim. It's your choice to replace it or give it a second try. If it doesn't seal on the second try just put it in the fridge.

Lid evaluation is based on the condition of the rubber seal band. If deeply indented, replace it. If any edge appears warped or dented, replace it. Again its basically your choice - your eyeballs. ;-) The goal is to not end up with unsealed jars after 2 processings.

Also make sure you aren't screwing the rings on too tight as that often causes seal failures. And don't overfill the jars as jams tend to boil over and create weak seals so increase your headspace a smidge if necessary. And don't mess with the jars lids or bands once out of the canner either. Some just take longer to seal than others and it is easy to break an early seal.

No you don't have to reheat the jam assuming an approved recipe in the first place.

Dave

PS: and feel free to vent ;-)

What name brand jars and lids are you using?

I'm using both ball jars and lids. I will thoroughly check the jars and lids and replace if necessary and try re-processing them this afternoon. I'm making another batch of (hopefully more successful) jam, so I'll have the canner going anyway. Worst case scenario, they'll keep in the fridge. I'm hoping my sealing curse lifts soon... ;)

Siobhan, I've been canning for, oh, 50 or 55 years, LOL, and sometimes I get a batch of lids that just don't seal. I don't know why, I don't know if it's a manufacturing error, it's not the jars, because they'll seal the second time. One year I got so disgusted with Ball flat lids that I ordered from a container place on line, just to get lids that sealed! Most times, though, I have no problem.

I have found that if you write to the Ball company and complain, many times they'll replace your "defective" lids.

Annie

Thank you for that, Annie, that made me feel a little better! All my batches I've made since I posted have sealed just fine, so I'm just keeping the failed ones in my fridge to eat myself! (I see a lot of almond butter and jam lunches in my future...) I think it was just Murphy's law -- for the first time ever, I decided to enter my jam in the county fair and I had to drop off my entry on Wednesday, but of course I didn't have any ripe peaches on my tree until Saturday! Oh well :)