Had the brakes around 3 years now, all ok

I don’t ride my bike much at all these days, maybe a few times a month

Last time I got it out the rear brake was binding on. It seems like the piston has crept out a little. I took the caliper off to have a look and both pistons are moving freely, it just seems that one piston wasn’t totally retracted into the caliper.

Any ideas why this may have happened? They have been ok for ages, and they are not seized. I really don’t want to try and bleed them if possible, it took me days to get it right last time

I had this too. Went for a ride on a 25C+ day and the rear began to drag, then lock up. I guessed that it was the fluid expanding in the heat, so loosened the bleed port on the MC and allowed a couple of drops out. Solved it completely with no recurrence.

First thing to do is just reset the pistons and see what happens tbh

The Ones have a slight quirk in that the expanding bellows in the reservoir butts against, and vents past, the handlebars. This isn’t usually an issue but with painted or softly surfaced carbon bars, it’s possible to get a pretty good seal there which stops the bellows working properly- and that can remove the brake’s ability to cope with expansion, and cause bleeding problems.

This seems to be a known issue with formula brakes. Took mine back to Merlin and they swapped them for Shimano XT, no quibbles. not been a problem since.

Mine did this when we had a hot spell in May. I just let a little fluid out of the bleed screw

Mine did this in the middle of a long ride. I actually had to remove the rear caliper and tie wrap it to the frame before carrying on with just a front brake . Letting a nads of fluid out cured the problem but made me a permanent convert to Shimano

Another Formula to Shimano convert here after a similar problem (and many others!). Piston retraction is poor as it is when new let alone with another issue thrown in…

Yep. Been there done that. Still think they’re ace brakes though.