I live in an old house in San Francisco. The shower setup is one of those with three knobs in a straight line. Hot water, shower diverter, cold water. On numerous occasions the shower has simply stopped working, sometimes with the water coming out of the shower in a slow trickle and sometimes with no water coming out at all. Sometimes turning things off and on slowly will yield better results.

Today I got it kind of working and when I tried to increase the cold water ratio I heard a loud clunk and water stopped flowing from the shower altogether.

This has happened and been "fixed" multiple times. However, it's my suspicion that it has never been properly fixed since it keeps happening. My questions for the forum are:

1) Any ideas as to why this is happening or why it keeps happening?
2) What questions should I be asking of the repair man to figure this out?

My gut is the landlord is hiring some amateur handy man to fix this because the proper fix is too expensive (a common theme in the building) and so it keeps breaking. I'd like to pin down exactly whats wrong so I can force him to fix it correctly. Please help...my pregnant wife had to bath this morning by pouring water over herself with a pitcher.

I would venture a guess that the washer has came loose from the end of the stem, possibly due to a worn screw hole in the stem, or screw. If at all possible a new stem would be the preferred method of repair, if a new stem is not available a new washer, and oversized screw may be the only option.