Toilet tanks normally take only a few minutes to fill back up after a flush. A slow-filling toilet tank means you will not be able to use the toilet as often, creating a problem for homes with few toilets and many people. Troubleshooting the problem yourself before calling a plumber may save you time and money on the problem.
Water Control Valve
The water control valve regulates the volume of water flowing into the toilet at any given time. If the valve is closed partway, it will slow the flow of water to the toilet's tank, causing it to fill more slowly. You can alleviate the problem and eliminate the water control valve as a culprit for the slow filling by turning the handle on the valve counterclockwise as far as possible. The valve will be completely open at this point, and the toilet should fill at a normal rate unless something else is wrong.
The flexible water line that connects the toilet to the water supply valve can also be the source of a slow-filling tank. Sometimes the water lines break down inside, causing obstructions to the flow of water. Previous owners of the house may have installed a water supply line that has a flow restrictor inside it. To tell if the water line is causing the problems, shut off the water supply at the valve, and drain the tank by flushing it and then sponging out the remaining water. Turn on a faucet and hold one end of the line so the water flows through it. If the water does not flow out the other end as quickly, then you know you need to install a new line.
The fill valve inside the toilet's tank can restrict the flow of water if it becomes clogged with hard water deposits or other debris. You must shut off the water to the toilet before you remove the valve's cap by pushing down on it as you twist it counterclockwise. With the cap removed, place your hand over the top of the valve and turn the water back on to flush out any debris. Turn off the water and twist the cap clockwise to replace it.
Low Water Pressure
If your toilet still fills slowly, you may have a bigger problem with the water pressure in your home. Try contacting the city to see if there are any problems with the water supply lines. A plumber can take a look at your home's plumbing to determine if any other problems exist that are affecting your home's water pressure.