Short answer
A toilet tank that won't fill, or fills slowly, is usually a partly closed shut-off valve, a fill valve clogged with sediment, a float set too low, or a kinked supply line. Open the valve behind the toilet fully, flush the fill valve to clear debris, and replace the fill valve if it still won't refill.
Updated 2026-10-09
Not sure this is your problem? Answer two or three questions and we’ll tell you what’s actually wrong. Run the diagnostic.
Check the shut-off valve first
The oval handle on the wall behind the toilet controls all the water going into the tank. If someone turned it during a repair, or it has been bumped, it may be only partly open. Turn it counter-clockwise until it stops.
If the valve won't move, don't force it. Old valves can snap or start leaking at the stem. That is a good reason to call a plumber.
Clear debris from the fill valve
Sediment and mineral flakes collect in the small opening at the top of the fill valve, especially in hard-water areas. The water still comes in, just slowly.
- 1Turn the water off at the shut-off valve.
- 2Remove the cap on top of the fill valve (on most modern valves, press down and twist a quarter turn).
- 3Hold a cup upside down over the open valve so you don't spray the ceiling.
- 4Turn the water on for a few seconds to flush grit out, then off again.
- 5Refit the cap, turn the water on, and watch it fill.
Check the float and water level
If the tank fills but stops well short, the float is set too low. Adjust the screw or clip on the fill valve until the water stops about an inch below the top of the overflow tube.
A float rubbing against the tank wall or the flush valve can stick and shut the water off early. Make sure it moves freely.
Look at the supply line
The flexible hose from the valve to the tank can kink when a toilet is pushed back, and older plastic or metal lines narrow inside over time. A new braided supply line is a cheap part and a quick swap.
When to replace the fill valve
If the valve is open, the line is clear and the tank still won't fill properly, the fill valve itself has worn out. Fill valves are close to universal and are one of the easier toilet repairs. If the whole house has low pressure, not just the toilet, that is a plumbing issue to have looked at.
Common questions
Why does my toilet take so long to fill?+
A slow fill is almost always restricted flow into the tank: a partly closed shut-off valve, debris in the fill valve, or an old supply line. Flushing the fill valve clears it in most cases. If the whole house has low water pressure, the problem is upstream of the toilet.
Is a toilet that won't fill an emergency?+
No, unless water is leaking onto the floor. You can still flush by pouring a bucket of water into the bowl. If the tank is also leaking, turn the shut-off valve clockwise to stop the water and get it repaired.
How long should a toilet tank take to refill?+
Most toilets refill within about a minute. If yours takes several minutes, start by flushing debris out of the fill valve.
Related
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