Why Does My Toilet Keep Running? (5 Fixes, Cheapest First)

A running toilet is the most common plumbing complaint in the country and one of the few where the DIY fix genuinely is the right answer. The parts are cheap, the water in the tank is clean, and there is nothing in there that can flood your house if you get it wrong. Start with the food colouring test. Drop a few drops of colouring into the tank and do not flush. Wait twenty minutes. If colour has bled into the bowl, water is escaping past the flapper. If the bowl is still clear, your problem is on the fill side. That one test splits the causes in half. ### Cause 1: A worn flapper (Most common) Probability: around 50%. Cost: $8-$15. The flapper is the rubber seal at the bottom of the tank. Rubber hardens and warps with age and chlorine, and once it no longer seats, water trickles into the bowl continuously and the fill valve keeps topping up. Take the old one to the hardware store — there are dozens of shapes and matching it in person is the only reliable method. ### Cause 2: The chain is the wrong length Probability: around 15%. Cost: free. Too short and the flapper cannot fully close. Too long and it tangles underneath and props itself open. You want just enough slack that the flapper sits flat with maybe half an inch spare. This costs nothing and takes about a minute. ### Cause 3: The float is set too high Probability: around 15%. Cost: free to $20. If the water level rises above the overflow tube, water pours down it endlessly and the toilet never stops filling. The waterline should sit about an inch below the top of that tube. Older ball floats bend down; newer cup floats slide on a rod with a clip or screw. ### Cause 4: A failed fill valve Probability: around 15%. Cost: $15-$25. If the tank fills and the valve never quite shuts off, or it cycles on by itself every few minutes, the valve is worn. Replacing the whole assembly is genuinely simpler than rebuilding it and costs about the same as a takeaway meal. ### Cause 5: A cracked overflow tube Probability: around 5%. Cost: $25 part, or replacement. Rare, but if the tube itself has split, water escapes below the normal line and nothing you do to the flapper or float helps. Inspect it for hairline cracks. On an old toilet this is often the point at which replacement makes more sense than repair. ### When to actually call someone - Water is appearing on the floor around the base, not just inside the tank - The toilet rocks when you sit on it - You have replaced the flapper and it still runs - The tank is cracked Those point at the flange or the seal underneath, and that is where a bad DIY job quietly rots a subfloor for months. ### Before you pay for a call-out A plumber will charge $100 to $250 for this, and most of it is the minimum service charge, not the $8 part. If you are getting someone out anyway, add it to that visit. Never book a dedicated call-out for a flapper.