Hi and welcome to FixYa. I am Kelly
You need to most likely change the inner valve cartridge. These Glacier Bay valves are sold at Home Depot and finding the correct replacement part will not be easy. Personal experience is to remove the old valve cartridge and walk into the store with part in hand. These valves use a ceramic insert / disc that locks into a groove of the cartridge. If the ceramic piece has drifted out of place they usually break off the inner locking tabs.
Should the store you visit not have the part you need... read these links:
Also read the 23 March article on this link near the bottom of the page:
Heading name is
Let me just add something........ check with your realtor about your HOME WARRANTY. This repair may very well be covered by the home warranty.
My honest opinion.... the sooner you get rid of the Glacier Bay Shower control the happier you will be. These controls were at one time Marketed under the in store name Pegasus.
I did not intend to ruin your day but... I do want anyone reading this to be advised of the consequences of buying inexpensive shore controls.
A word of advice when purchasing a new control valve. Pay for the good name ONCE and make sure the repair parts are in the same store where you make the purchase. It will cost you less in the long run. Have the sales person show you the repair parts for the MODEL that you are thinking of buying. Delta, Moen, Price Pfister are 3 names that have been around a long time and have repair parts readily available in the marketplace. (end rant)
Thanks for choosing FixYa,