Why does my toilet keep running?

A toilet that runs constantly — or refills on its own every few minutes — is almost always a worn flapper or a faulty fill valve inside the tank. It's a small part failing, but a big water bill: a running toilet can waste 200+ gallons a day. The parts cost $10–$25, and this is the most DIY-friendly plumbing fix there is.

Likely causes

• Worn flapper — The rubber seal at the tank bottom warps with age and chlorine — water seeps into the bowl silently.
• Faulty fill valve — The toilet runs on after flushing or the valve hisses — the shutoff mechanism is worn.
• Chain or handle problem — A chain that's too long or kinked holds the flapper open.
• Cracked overflow tube — Water spills into the overflow — less common, needs a new flush valve assembly.

What you can check yourself

• Drop food coloring in the tank: if color appears in the bowl without flushing, the flapper leaks. Replace it — a 15-minute job, mostly no tools.
• Check the water level: it should sit about an inch below the overflow tube; adjust the fill valve if water spills over.
• Jiggle test first: if jiggling the handle stops the running, it's the chain or flapper alignment.

Typical cost

DIY parts run $10–$25. A plumber in Denver, CO typically charges $150–$350 for the repair visit; full toilet replacement runs $350–$700 installed.

When to call a pro

Water on the floor at the base, a toilet that rocks, or a sewer smell — that's a wax-ring or flange problem, not a flapper. Call before the subfloor rots.

Plumber pros in Denver, CO

• Rk Mechanical · 3800 Xanthia St, Denver, CO · +13035769696
• Eagle Pipe · 1228 15th St Ste 200, Denver, CO · +17134647473
• Assured Backflow · 1330 Logan St, Denver, CO · +13036806011
• Golden Hands Plumbing & Heating · 1240 East Colfax Avenue, Denver, CO · +1-720-602-6975
• Go With the Flow Plumbing · Denver, CO · +12148508687
• US Plumbers Home Service Denver · 2020 Lawrence St #1025, Denver, CO · (720) 640-4086
• Denver Sanitary · 3161 Walnut St, Denver, CO · +13032950331
• City Emergency Plumbing Denver Services · 3600 E 40th Ave, Denver, CO · (719) 851-3128

Get free quotes from Denver, CO pros →

Data by Servik — verified local pros from official license records and public sources. Cost figures are typical ranges, not quotes; a pro's written estimate is the real number.