My hope minis are long in the tooth , and the front disc is locking on all the time . It appears that the piston isnt returning in the calliper body . is it just a case of giving them a good bleed to cure it ? or is there something else causing the problem ?
Cheers

The pistons need cleaning and lubing. Remove pads – pump the pistons part way out. Spray with brake cleaner and scrub with a toothbrush, lube either with brake fluid or preferably red rubber grease. Work pistons in and out a few times.

If that don’t work strip clean and rebuild with new seals or even new pistons. Old alloy pistons can be rubbed down with oiled emery paper / wet and dry if corroded. Damaged phenolic pistons need to be replaced.

Or send them to hope for their very reasonable and effective servicing.

as TJ said

I had a sticky piston issue easily soreted

on mine I removed the pads pumped the pistons out and soaked in a light lube and pushed them back in, this was repeated several times till both pistons moved the same ammount when the lever was pulled in. Cleaned off all traces of oil refitted the pads. purfect

Be very cautious what lube you use – some types will cause the seals to swell and make the sticking worse hence I use either brake fluid or the red rubber grease.