A PVC ball valve, and add a threaded coupler to attach the supply line from sink.
Obstruction in the hot water supply line, bad valve, or broken water line. Drain system and remove valve cartridge, open hot supply to blow out line and see if water comes out. If it does than you have a bad cartridge, if not broken line that needs to be repaired.
The water supply line attaches to it on the bottom of the tank. The actual valve is at the top of this tube.
Have the new valve in hand. Cut the toilet water supply off at the commode, or even at the street meter box.Remove water tube or pipe supply and old flush valve. Install new valve and new supply line if required.
This activates a solenoid (electromagnetic switch) on the water inflow line, which opens the valve. When the valve is open, pressured cold water from your regular home supply comes into the shower... This valve is controlled by the huge temperature dial that you crank to make the water hotter or colder as needed.
Did you remember to turn the supply line back on? Was there a plug that needed to be removed before connecting it?
Check the angle stop. Check the supply line. Then check the fluid master valve.
Check if the water supply line valve underneath the sink is on or off .."On" will be turning counterclockwise ,If not look for the hot water heater and make sure the water supply valve is turned on.
A thermally controlled mixing valve is connected between the hot supply line and the return line, tempering the hot supply with the cooler return water.
Try to mechanically restrict the supply line, by partially closing the closest valve to the fountain. If you do not have a valve and the supply lines are of a flexible tubing try clamping the hose to reduce the diameter.
It is where the supply line is attached to a water line. May be under the kitchen sink or in the basement under the refrigerator in the closest supply line. Should be a hot water line. Hot water because most of the minerals stay in the water heater and the water in the supply line will be cold from sitting. Someone may have put a shutoff at the floor behind the refrigerator, but I doubt it.
It will be close to the inside wall where the water supply passes into the house from the line going towards the water meret.
The shut off valve.