If the electrics are OK it maybe the motor a bit lazy or dry mechanism/slide in the door. Get someone to hold the switch down and see if you can slide it down by hand. If it frees off keep doing it up and down and see how you go. You may have to take the door panel off though to free it off. Why not phone the garage and ask them what they did?
Although unlikely at this time of the year, tree sap can also cause it on the rubbers.