The handle operates only the water flow to the shower head. It will not push in far enough to turn the water all the way off. What's wrong?

The handle operates only the water flow to the shower head. It will not push in far enough to turn the water all the way off. What's wrong?
Shower faucet-Moen 1988

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The handle operates only the water flow to the shower head. It will not push in far enough to turn the water all the way off. What's wrong?

You have a Moen #2400 with some trash caught in the diverter seat that's not allowing it to close and seat.
Remove the knob and face plate. Unscrew the large nut and diverter assembly and pull it out. Clean out the diverter seat and flush it out. Reassemble and test. Good luck, Tom

I have this shower single handle control valve that is leaking. I tried to find the replacement in homedepot and lowe's but they don't carry the type anymore. Where could I get the replacement cartridge for my shower valve. It was installed originally when my house was built in 1988. Any assistance is greatly appreciated.

v/r
Ron