Toilet Keeps Running
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Quick answer: First find out whether it’s the fill valve (water rises so high it spills into the overflow pipe) or the flapper / flush valve (water slowly leaks from the tank into the bowl). Fluidmaster says to flush debris out of the fill valve, then replace it if needed; if the tank level drops, replace the flapper first, then the flush valve.
Test order: easiest & free first
- Check where the water goesFREE · 5 min
Turn the water on and look inside the tank. If the water level rises so high it drains into the overflow pipe, the fill valve is the problem (Fluidmaster). - Do the drain-down testFREE · 10–15 min
With the tank full, turn off the water to the toilet and mark the water level. Wait 10–15 minutes; if the level drops below your mark, water is leaking past the flapper (Fluidmaster). - Flush debris out of the fill valveFREE · 10 min
Fluidmaster: dirt and debris can lodge inside the valve. Turn off water and flush, remove the valve cap (on Fluidmaster valves: hold the float cup and shaft, twist cap and arm counterclockwise 1/8 turn), hold an upside-down cup over the opening and turn the supply on full for 10–15 seconds, then reassemble and test. - Replace the fill valvePART
If cleaning doesn’t fix the overflow, Fluidmaster says replacing the fill valve should resolve it. - Replace the flapperPART
If the drain-down test shows a leak, Fluidmaster says to replace the flapper first, as it is the most common problem. Check whether you need a 2″ or 3″ flapper. - Replace the flush valvePART
If the tank still drains down after a new flapper, Fluidmaster recommends replacing the flush valve.
⚠ Safety: If the toilet is running and there’s water on the floor, turn off the water immediately and check whether it’s coming from the lid/lever area or the bottom of the tank (Fluidmaster). Fluidmaster also warns not to use in-tank drop-in bowl cleaners containing bleach or chlorine; they can damage tank parts and may cause flooding.
Parts to check
| Part | Part number | |
|---|---|---|
| Fill valve | Fluidmaster recommends 400H PerforMAX | Check price [PLACEHOLDER – no affiliate link] |
| Flapper, 2″ | Fluidmaster 502 | Check price [PLACEHOLDER – no affiliate link] |
| Flapper, 3″ | Fluidmaster 513A or 5403 | Check price [PLACEHOLDER – no affiliate link] |
| Flapper, 2″/3″ convertible | Fluidmaster 523A Super Flapper | Check price [PLACEHOLDER – no affiliate link] |
| Flush valve | Fluidmaster K-507A-008 (2″) or 540AKR (3″) | Check price [PLACEHOLDER – no affiliate link] |
We only list part numbers confirmed by a cited source; the numbers above are Fluidmaster’s own recommendations. Toilets vary, so confirm your flush valve size (2″ or 3″) and toilet type before ordering.
💡 Water on the floor from the tank bottom? Fluidmaster says to change the tank bolts and washers.
Watch it done
Video by Fluidmaster Toilet Repair Videos on YouTube. FixCode Guide isn't affiliated with this channel.