If you find that your toilet tank won't fill with water, the problem could involve the water supply for the toilet or the toilet fill valve. Water line ruptures or other troubles in your area could cause an interruption in your service. The fill valve in the tank connects to your home's water supply and fills the toilet as needed. If the water is working in the rest of the house, a faulty fill valve could be stopping your toilet tank from filling with water.
Check the water supply for the other fixtures, such as kitchen and bathroom sinks. If these aren't working, there is a problem with your main water supply. Call a plumber to help determine where the problem is with your main.
Check that the water supply for your toilet is working. Locate the water-supply valve behind the toilet; a hose or pipe connects this valve to the toilet tank. Open the knob at the end of the valve all the way by turning it counterclockwise.
Rotate the water supply for the toilet knob all the way to the right to cut off the water for the toilet. Remove the toilet lid. Flush the toilet. After the flush, continue holding down the lever until all the water inside the toilet is gone. Use a towel to wipe up any extra water.
Place another towel on the floor underneath the tank. Unscrew the coupling that connects the hose or pipe to the tank, using the pliers. Remove the plastic retaining nut located above the hose or pipe coupling. Remove the toilet fill valve from the tank.
Insert a new fill valve into the tank. Make sure that the gasket sits flush on the bottom of the tank. Hold this in place with one hand, or have an assistant hold it for you.
Tighten the plastic retaining nut on the underside of the new fill valve. Secure it in place with the pliers.
Wrap the threads on the new fill valve with plumber's tape. Trim off any excess. Reconnect the water-supply pipe or hose coupling to the wrapped threads. Tighten the connection with pliers.
Turn on the water-supply knob by rotating it to the left. Watch as the tank fills up and check for leaks. Tighten any couplings with the pliers as needed. Flush the toilet and ensure that everything works correctly. Replace the lid.
Do not try to repair a broken fill valve. Many older fill valves do not incorporate antisiphon technology.