Brake pads constantly touching the rotor because piston is not moving back I recently replaced the brake pads on my hydraulic disc brake. The brakes are a Tektro Draco 2. Now the new pads are constantly touching the rotor. 



This is how it looks like with caliper unmounted. Notice the left piston is constantly sticking out:



I tried spreading the pistons with a spacer. I left it in there for 3 hours



But still, the left piston comes out again. I'm thinking about buying a service kit to bleed the system. Will that help?
I left the spacer in overnight. The Piston now goes all the way back. Guess I was just too impatient :)