Once other cause of a running toilet is a loose or worn flapper. You can tell if the flapper is causing the problem if the noise stops when you jiggle the handle or press down the flapper. You can adjust the chain by a couple links - it might be holding the flapper open slightly. Or, replace the flapper by lifting and hooking a new, correctly sized, flapper in place.

If you want to know why your toilet tank fills too slowly, or not at all, check the water supply valve. Make sure it’s open – it works just like a faucet handle. Check the hose between the valve and the toilet tank. If this supply line is kinked or damaged, replace it.

If you checked the supply valve and supply line, and they’re working fine, you may need a new fill valve. A fill valve is simple to install. The specific instructions will depend on the product you use. This is a good time to replace and old valve with a newer water saving device.

If you’re wondering why your toilet won’t flush, or why you have to hold down the handle to get it to flush check the arm connecting the flush lever to the flapper chain. Replace it if it’s broken, and reconnect the chain. Check the chain and tighten it if there is too much slack.

Another reason your toilet may not flush right is the flapper. Measure the flush valve to see if you have the right size flapper. A 2-inch opening is very common, but some brands are 3-inches. You can also find universal flappers that eliminate some of the guesswork.

If the toilet still won’t flush, you might need to reset the tank water level. Twist the float cup on newer fill valves to adjust the water level. Or, on a traditional style float, you can bend the arm attached to the lever and the flapper chain, slightly to adjust it.

Find the location of the leak to diagnose where it’s coming from. Water on the floor or ceiling under a toilet, sewer smells, or damaged flooring, could mean you need to replace the wax ring under the toilet. See "How to Install a Toilet," to learn how to complete this repair.

If you notice a leak between the tank and the bowl, drop some leak detection tablets into the toilet tank to check. Don’t flush the toilet. Check back after about 30 minutes. If colored water shows up is between the tank and bowl, Try tightening the nuts under the tank. Or, replace the gasket between the tank and bowl.

If you think the toilet bowl is leaking, drop leak detection tablets in the bowl. If colored water seeps through to the outside, unfortunately there’s no way to patch it. You’ll need to replace the whole toilet.

If you’re replacing the flapper often, it may be drop-in toilet cleaning tabs that are corroding it. Replace your old flapper with a chlorine-resistant flapper. Or, switch to an in-the bowl cleaning system.

When you need new parts, it helps to know the toilet’s age and brand. Look for the info stamped on the inside of the tank.