We purchased an old house that has what appears to be a custom shower stall, no tub. There are 2 knobs (1 hot, 1 cold) and a shower head protruding from the wall -- no name brands on anything. The problem, if we just turn the knobs off manually - the showerhead still flows water, we have to use a wrench to turn the knobs further to get the showerhead to stop flowing water after we shower. Is there anything we can do to repair?