I can't get the little knob that turns on the shower and turns off the water in the tub to stay up,I took off the showerhead that is not the problem The water does not go up to the shower unless I place a rag over the pipe and turn the water on.

That little knob stays in the upward position by the suction of the water while rushing upwards to the shower head.

Most probably there is some calcium deposit or other material on the rubber that prevents the blocking of the water outlet towards the bath.

Just try that direction of thought to solve the problem.

:)

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The diverter in your valve is not working. Try to give us a brand and or model number of that valve. When you pull up on that knob does the water to the tub slow dramatically? Does it ever come out of the shower head after holding the knob for awhile?

The solution is not clear enough.

There are three knobs; first your turn on the hot and cold knobs and then you open the middle knob to activate the shower head. It just makes a "shuddering" sound but the water does not come out.