Frozen front brake

My Jimnys front ledt brake caliper is frozen thecaliper piston wont return unless you push it back but its not rusty. Any ideas?

How would i tell if it was that?

Caliper pistons don't return as such and need to be pushed home when changing pads for example, the caliper piston squeezes the pads on to the disc under pressure then stop gripping the disc when the pressure of the brake pedal is released.

The pads will always have a very slight drag on the disc unless your disc is warped then the piston will get pushed back.

My nearside front brake was siezing on this weekend, i took the slider tubes out, cleaned them with wire wool and regreased them, the top one was partially siezed, i then pumped the caliper piston out (4 pedal pumps only) repeatedly and re-compressed the piston back in and at the same time rotated the piston while red greasing the piston.

Not advising you to do this unless you know what your doing, my brake is now free and NOT leaking and i've done about 60mls since.

If your brake hose has collapsed, release the bleed nipple and the wheel will rotate freely.
If the caliper has siezed the wheel will not rotate freely when the bleed nipple is released.

The piston retracts when the brake pedal is released and the twisting of the piston inner seal has enough elasticity to pull the piston back as there is no pressure from the fluid to keep it out against the pads.

In most cases over the years the inner seal becomes less elastic and gets a bit stiff and therefore does not have the elasticity to pull back the piston off the pads. The piston sticks out against the pads

I find replacing the seals lasts say a year and that a replacement caliper in a lot of cases they are new lasts a lot longer. That is both Jimny's MX5's and Imprezas.