Thanks. I never would have found the forth screw!
You can dismantle the swivel at the other end of the hose enough to expose the contact rings. They can get dirty enough to break the electrical contact. Cleaning the contact rings fixed my problem.
To dismantle: look up the plastic on each side of the group of three electrical prongs. Near the top of that you will see a small rectangular hole. With a small screwdriver push in the tab in each hole while pulling down on the cylindrical plastic -- the part that would insert into the canister. (It helps to have three hands to do this.) It comes apart easily. THe little assembly with the three prongs and three brushes falls out. It's all easy to clean and reassemble. To reassemble place the brushes and prongs in the right place and slide the cylindrical plastic piece back on.
L Shar
February 2009