Front Pads Binding

[ratkinsonuk]

I changed my front pads recently, but accidentally popped one of the pistons out of the caliper whilst cleaning. I've bled the brakes and they're working fine, but the pistons refuse to retract and the pads are binding, so the wheel won't rotate freely.

I've come back from a 2000 mile European trip expecting it to have sorted itself, but no joy.

Any ideas what I can do to get the calipers to release?

Cheers