Need help with front brake problem

The front disc seized on and by the time I stopped the disc was glowing a bright red in the dark of the night and smoke was billowing from around the caliper. After about 15 minutes, the wheel could turn and very slowly I rode home only using the back brake.

When I used the brake at home the wheel would lock and the brake would only release over some minutes, unless I opened the bleed valve.
I changed the brake hose as I thought it might have collapsed but then had no pressure at the the lever.
I've changed the master cylinder but still no pressure.
I can bled the fluid through using a vacuum pump. but still can't get any pressure or a brake.
Can anyone identify the problem?
Is it the caliper or am I doing something wrong?

Has the piston seized in the caliper?

sorted, I think

Pull off the caliper and blew out the piston with an airline. Using a piece of thin plastic, I was able to get the piston back in after inspection. Using the airline and a stopper block of wood, I could move the piston freely in and out.
Reassemble everything and still no brake.
Went back to the original brake hose, but it wouldn't bleed through, so that would seem to be the original problem.
With the HEL brake hose in place, I removed the bleed valve and filled the caliper with fluid. With the bleed valve back in place, I used a vacuum bleeder and after refilling the master cylinder twice I got a brake.