I have Formula T1S disc brakes (2014 or 2013 model). One day when it was quite hot (in the 30s), but otherwise on a very mild ride on bike paths with kids, the brake started rubbing constantly by itself, grabbing the wheel quite strongly as if on both sides, giving me significant resistance (couldn't even spin the wheel freely). I couldn't reset it using normal disc brake alignment procedure (loosen bolts, hold lever, tighen while holding).
Upon more careful examination, when I removed the brake pads at home, it turned out the pistons inside are pushed inwards, not flush with the brake body, and I can't push them back outwards - I mean both at the same time: when I push one outwards, the other goes in.
How to diagnose how to proceed from there? I haven't serviced these brakes since I bought the bike 5 years ago and in fact it was my first bike with disc brakes, I don't have a lot of experience here. Other answers and various videos suggest a full bleed procedure which means I should probably bring the bike in to the LBS, as I don't fancy buying a full bleed kit to do something once every 5 years... and I don't even know if it would solve the problem.