A malfunctioning toilet can cause both inconvenience and an increase in your water bill. The most common problems with a toilet can be found inside the tank. The inner workings of the toilet tank control how the toilet flushes, how it shuts off after each flush and the water level. Repairing or replacing the inner workings of a toilet is not too difficult. You can repair some problems yourself if you know the common causes for a toilet to malfunction and how to replace the related toilet plumbing.
Put food colouring in toilet tank--it's an old plumber's trick, and one of the easiest ways to determine whether or not your toilet is leaking. Simply put some food colouring in the tank. Do not flush. If the colour shows up in the toilet bowl, the flapper valve needs to be replaced.
Replace flapper valve. The food colouring has shown you that your flapper valve is leaking, and now you must replace it. Turn off the water to your toilet and flush the toilet, which will empty the water from the tank. The flapper valve is the round rubber part at the bottom of the tank; it's usually red, though some are black. Most flapper valves have two little "wings" on either side from which you unhook it. (Some flapper valves may be connected by a circle of rubber on the top of the valve.) Take this to your local hardware or plumbing supply store. Replace the new flapper valve using the hooks. (Note: All new flapper valves have both the little "wings" at the bottom and the circle of rubber at the top. If you do not need the circle of rubber at the top, cut it off with scissors.)
Replace the ball cock. The ball cock, which may also sometimes be called the water inlet valve, is on a shaft inside your toilet tank. It slides down when the toilet is flushed, then rises as the tank refills. A well-functioning ball cock should, at some point, stop the water from rising, which makes the water in the tank stop running. If that's not the case--and the water in the tank continues to run, which can cause an increase in your water bill--the ball cock needs to be replaced. To replace, turn off the water to your toilet and flush to empty the water from the tank. Use a sponge or a rag to remove the rest of the water from the tank. Loosen the nut on the water supply line on the outside and underneath the toilet tank. Then remove the nut to the ball cock, located in the same place. Lift the ball cock out of the tank. A Fluidmaster brand is recommended; however, you can take the worn ball cock to your local hardware or plumbing supply store to purchase a replacement part. The easiest way then to replace the ball cock is to follow the instructions included with your replacement parts. Finally, adjust the ball cock to the proper water level.
Check the water supply line. After replacing your ball cock and before turning the water back on to your toilet, check your water supply line while you already have it loose from your toilet tank. If it looks old and worn, you may want to replace it, too. Take the water supply line loose from the other end, usually at the cut-off valve to your toilet. Replace it with the same length of line.
If you require the services of a plumber, ask people you know for recommendations. Check the link for Fluidmaster under "References" for diagrams of the inner workings of a toilet.
Some plumbing problems concerning your toilet, such as a cracked bowl or worn seal, may require more expertise than you possess. In such cases, check with a licensed and experienced plumber.