A constantly running toilet is almost always a worn flapper, a faulty fill valve, or a misadjusted float. It is also a quiet water waster: a running toilet can waste hundreds of gallons a day. This guide explains how to diagnose it and stop it.
The flapper
The flapper is the rubber disc at the bottom of the cistern that seals the flush valve. When it warps, blisters or stiffens, water leaks from the cistern into the bowl and the fill valve keeps topping it up. Test it with food colouring: put a few drops in the cistern, wait 15 minutes without flushing, and look for colour in the bowl. Colour means the flapper is leaking. Replacing it is a simple job: turn off the water, flush to empty the cistern, unhook the old flapper and fit a new one of the same size, with a little slack in the chain.
The fill valve and float
Set the water level first
If water is running into the overflow tube, the water level is too high. Adjust the float so the water sits about an inch below the top of the overflow tube: bend a ball-float arm down slightly, or slide a cup float down on the fill valve. If the fill valve hisses, fills slowly or will not shut off, it may be clogged with sediment or worn out. Denver's soft to moderately hard water leaves scale, and scale shortens the life of fill valves.
The overflow tube
A cracked or low tube
If the overflow tube itself is cracked or set too low, water runs into it constantly. Check that the tube is intact and at the right height. A cracked tube needs replacing, which means removing the flush valve: a bigger job than a flapper swap, and one where a plumber is often the faster answer.
When to call a plumber
Once the flapper, the fill valve and the overflow tube have all been checked and the toilet still runs, the cause is no longer one of the three usual parts. What is left is the flush valve itself, a cracked overflow tube, or the supply — and swapping more cistern parts will not find it. That is the point to call a plumber rather than keep adjusting. See toilet repair, toilet installation and our step-by-step guide to fixing a running toilet with simple adjustments. Call (720) 599-7253 if the steps above do not stop it.