The thermostatic shower button is connected to the shower diverter valve. The diverter valve diverts water from one path to another path. If the thermostatic shower button is stuck, it is most likely because the diverter valve is malfunctioning. This is relatively simple to check and adjust.
Step 1: Remove the Valve
First, you must remove whatever is blocking the valve, which could be the faucet or knob. These can be removed easily with a screwdriver or wrench. Also, remove any other fixtures mounted around the faucet that impede your entrance to the diverter valve. These are sometimes removeable without any additional tools.
Step 2 - Diagnose
If the diverter valve is simply out of line, adjust it so that it is once again in line with the button. If it is corroded or deteriorated, you will have to replace the valve entirely.
Step 3 - Replacement
If you decide to replace the diverter valve, make sure that you purchase one that has all of the components of the original. With a new diverter valve and some tape, your valve and your button will be fixed in no time.