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If your toilet randomly runs for a few seconds, takes forever to refill, or hisses constantly after flushing, the fill valve is almost certainly the problem. After the flapper, the fill valve is the second most common toilet failure — and it’s just as easy to fix yourself. I’ve replaced hundreds of fill valves. Here are the ones worth buying.
| Product | Best For | Price |
|---|---|---|
| Fluidmaster 400A Fill Valve | Best Overall | ~$12 |
| Korky 528MP PerforMAX Fill Valve | Best for Quiet Fill | ~$16 |
| Fluidmaster 400CRP14 Complete Kit | Best Complete Fix | ~$18 |
How to Know It’s the Fill Valve and Not the Flapper
Most running-toilet fixes start with the flapper, and a lot of people land here because they already swapped the flapper and the toilet still runs. Here’s the 30-second way to tell the two apart. Put a few drops of food coloring in the tank and don’t flush. Come back in 15 minutes: if color shows up in the bowl, water is sneaking past the flapper or the flush-valve seat. If the bowl stays clear but you still hear the toilet hiss or cycle on by itself, the water is running out the overflow tube — and that’s the fill valve failing to shut off. A fill valve that won’t stop running, fills in surges, or hisses between flushes is worn out. Replace it with one of the picks below.
Best Overall: Fluidmaster 400A Universal Fill Valve
anti-siphon design · adjustable height 9-14 in · universal fit (most toilets) · includes refill tube, shank washer, locknut & clip · 5-year warranty
The Fluidmaster 400A has been the standard toilet fill valve for decades. It fits virtually every toilet made in the last 40 years, installs without tools, and adjusts for both tank height and water level. Anti-siphon design meets all code requirements. At $12, this is one of the best value repairs in all of home plumbing — it’s the first thing I grab when a toilet is running and the flapper checks out fine.
- ✅ Universal fit — works with almost any toilet
- ✅ Adjustable height and water level
- ✅ Anti-siphon / code compliant
- ✅ No tools required for installation
- ✅ Best-selling fill valve in the US
- The anti-siphon design is code-approved and prevents fresh-water supply contamination.
- Height adjusts from 9 to 14 inches to fit most standard toilet tanks.
- It ships with the refill tube, shank washer, locknut and clip needed to install.
- It is not supported on certain flapperless or one-piece toilets.
- It replaces only the fill valve, so a leaking flapper would need to be bought separately.
Verdict: Best for a reliable, universal fill-valve swap on most standard two-piece toilets.
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Best for Quiet Fill: Korky 528MP PerforMAX
anti-siphon · adjustable height 7-3/4 to 13-1/2 in · quieter than standard fill valves · tool-free install · fits Kohler, TOTO, American Standard & all brands · 5-year warranty
If the fill noise bothers you — especially for a bedroom bathroom — Korky’s PerforMAX fills the tank more slowly and quietly. It also delivers a stronger flush by optimizing the fill rate, useful for older toilets with weak performance.
- ✅ Significantly quieter than standard valves
- ✅ Improves flush on older toilets
- ✅ Universal fit
- ❌ Slightly more complex installation
- It runs quieter than standard fill valves during the refill cycle.
- Height adjusts from 7-3/4 to 13-1/2 inches and fits Kohler, TOTO, American Standard and other brands.
- Installation and adjustment require no tools.
- It is designed for 1994-or-newer toilets rated 1.6 gpf or less, so it is not ideal for older high-volume tanks.
- It replaces only the fill valve and does not include a flapper.
Verdict: Best for anyone who wants the quietest possible refill in a modern low-flow toilet.
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Best Complete Fix: Fluidmaster 400CRP14 Kit
includes 400A anti-siphon fill valve + a 2-inch flapper · adjustable height 9-14 in · fits most 2-inch flush-valve toilets · Microban-treated flapper resists hard water & bacteria · 5-year warranty
Not sure if it’s the fill valve, the flapper, or both? This kit includes both parts plus a supply line — everything needed for a full rebuild. For a toilet that hasn’t been serviced in years, replacing all three at once makes sense and costs about the same as a single service call.
- ✅ Fill valve + flapper + supply line
- ✅ One kit fixes all common causes of a running toilet
- ✅ Saves a second hardware store trip
- The kit pairs the 400A fill valve with a 2-inch flapper to fix both running and slow-filling issues at once.
- The flapper uses corrosion-resistant Microban material to resist hard water and bacteria breakdown.
- It fits most 2-inch flush-valve toilets and installs in about ten minutes.
- The included flapper only fits 2-inch flush valves, not 3-inch ones.
- It is matched to standard toilets, not specialty flapperless models.
Verdict: Best for a complete tank rebuild when both the fill valve and flapper need replacing.
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How to Replace a Toilet Fill Valve
- Shut off the supply valve behind the toilet.
- Flush to empty the tank, sponge out remaining water.
- Disconnect the supply line from the bottom of the tank.
- Unscrew the locknut under the tank (counterclockwise) and lift out the old valve.
- Set the new valve height — top should be 1 inch below the overflow tube.
- Insert through the tank hole and hand-tighten the locknut underneath.
- Reconnect the supply line and attach the refill tube to the overflow pipe.
- Turn water on slowly, let tank fill, adjust water level if needed.
Plumber’s tip: Set the water level 1 inch below the top of the overflow tube. Too high and water runs into the overflow continuously — looks like a flapper leak but isn’t.
FAQ
How do I know it’s the fill valve and not the flapper?
Put food coloring in the tank. If color appears in the bowl without flushing, it’s the flapper. If the water level in the tank looks fine but you hear hissing or constant running, it’s the fill valve.
My toilet hisses constantly. Is that the fill valve?
Yes — a constant hiss is almost always the fill valve. Either the valve seal is worn or the water level is too high and constantly running into the overflow tube.
Can I replace a fill valve without a plumber?
Absolutely — it’s one of the most beginner-friendly plumbing repairs there is. No soldering, no special tools. If you can shut off a valve and use pliers, you can do this.
Bottom Line
The Fluidmaster 400A is the right call for 90% of toilets. $12, 15 minutes, fixes the most common cause of a running toilet. You’ll save that money back on your water bill within a month.
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