How to Stop a Running Toilet (Flapper Replacement) in Denver, CO
Denver's mountain water is soft to moderately hard, averaging about 105 mg/L, so scale is rarely what keeps a toilet running here. It is more often a flapper that has hardened or warped, a chain that catches, or an aging fill valve. In older Denver homes, the shut-off valve behind the toilet can also be stiff, so check it before you start.
📺 Video Tutorial: https://youtu.be/KXzYIhhfOuA
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📋 Step-by-Step Manual
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Step 1: Turn off the water supply
Turn the shutoff valve behind the toilet clockwise until it stops, cutting off water to the tank.
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Step 2: Drain the tank
Flush the toilet and hold the handle down to let as much water as possible drain from the tank.
💡 Tip: Sponge out the last inch of water so you're not reaching into a full tank. -
Step 3: Detach the old flapper
Unclip the flapper's ears from the pegs on either side of the overflow tube, then disconnect the chain from the flush lever.
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Step 4: Match and buy the right flapper
Bring the old flapper with you (or match the brand/model) — flapper size and shape vary between toilet brands like Kohler, American Standard, and Toto.
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Step 5: Install the new flapper
Clip the new flapper onto the same pegs, then attach the chain to the flush lever with a little slack — about 1/2 inch when the flapper is closed.
💡 Tip: Too much chain slack causes double-flushing; too little keeps the flapper from sealing, which causes the running-water sound. -
Step 6: Turn the water back on and test
Open the shutoff valve, let the tank refill, and flush a few times to confirm the toilet shuts off completely and doesn't keep hissing.
📍 Denver Tips for This Repair
- Denver's water is soft to moderately hard, so look first at the flapper itself. A flapper that feels stiff or warped will not seal, even on a clean seat.
- In older Denver homes, test the toilet's shut-off valve before you start. If it will not turn or leaks at the stem, use the main shut-off and plan to replace the valve.
- Swapping a flapper or fill valve is a general repair, which Denver lists as not needing a building permit.
❓ Denver Repair FAQ
Do I need a permit to fix a running toilet in Denver?
No. Replacing a flapper or fill valve is a general repair that does not alter the plumbing system, which Denver lists as work that does not need a building permit.
Is hard water why my Denver toilet keeps running?
Probably not. Denver Water's 2025 sampling averaged about 105 mg/L, so scale builds slowly. A hardened flapper, a snagging chain, or a worn fill valve is more likely.
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More Denver Repair Guides
Denver Housing Context
Denver's housing spans more than a century. About 16% of homes were built before 1940, including the brick bungalows and Denver Squares of older neighborhoods, and roughly a third date from before 1960. At the same time, about a quarter of the city's housing has been built since 2010. In the older homes, original drain lines, aging shut-off valves, and early electrical service are common. Freezing winter nights add the risk of frozen pipes in exterior walls and crawlspaces.
Denver Water Quality
Denver Water draws from mountain sources, including the upper South Platte and Blue rivers, Bear Creek, South Boulder Creek, and Fraser River tributaries, stored in reservoirs such as Dillon and Cheesman. The utility describes its water as soft to moderately hard. Its 2025 sampling averaged about 105 mg/L total hardness (roughly 6 grains per gallon), ranging from about 55 to 124 mg/L, with the northern system softer than the southern one. That means some mineral scale, but far less than in desert cities.
Municipal Permit & Code Guidance
Some plumbing and electrical work in Denver may require a permit or inspection under local building code, especially anything involving new supply lines, panel upgrades, or moving fixtures. The steps below cover minor, homeowner-performed maintenance only — for any work that may require a permit, contact the Denver Community Planning and Development before starting.
For this repair in Denver: Swapping a flapper or fill valve is a general repair that does not change the plumbing system, which Denver lists as not needing a building permit. A wastewater permit can still apply to some projects, so check if you are changing drain lines.
Denver issues homeowner permits only to the legal owner who lives in a single-family home (not a condo, townhome, or duplex, and not a trust or LLC). The owner must do the work and pass a free homeowner exam before doing plumbing or electrical work.
Permit notes last reviewed October 2026 against official city and state pages. Rules change, so confirm before you start.
Visit Denver Community Planning and Development →FixOrPro AI is not a substitute for local code review. Always verify permit requirements with your local building department before performing electrical, plumbing, or structural work.