Toilet Tank Won't Fill After Flushing — Fill Valve Cap, Float & Supply Checks

Common Symptoms

• Tank empties during the flush but no refill sound follows
• Water level stays at the bottom of the tank after flushing
• Tapping the fill valve or moving the float starts the refill temporarily
• Toilet will flush only once unless you manually add water to the tank
• Refill starts very late or only trickles in after a long pause
• Other fixtures still have normal water pressure

Most Likely Causes

1. 1

   Fill Valve Stuck Closed After the Flush

   Modern fill valves use a diaphragm and cap assembly that should open as the float drops. If that mechanism sticks, the valve never begins refilling even though the tank is empty. A light tap on the cap sometimes makes it start again, which is a classic sign the valve is worn out.

2. 2

   Debris in the Fill Valve Cap or Inlet Screen

   Rust flakes, mineral grit, or supply-line debris can lodge in the valve cap or inlet screen and stop the fill valve from opening properly. This often happens after plumbing work, water shutoffs, or in older homes with sediment in the lines.

3. 3

   Float Cup or Float Arm Jammed in the Wrong Position

   If the float binds against the tank wall, refill tube, or valve shank, it may not drop far enough to open the valve after a flush. On older ball-float toilets, a bent arm can do the same thing. The tank looks empty, but the valve still 'thinks' it should be shut.

4. 4

   Partially Closed or Restricted Shutoff Valve

   The shutoff valve behind the toilet may be partly closed, internally corroded, or clogged enough to starve the fill valve. In some cases the valve lets just enough water through for a slow hiss, but not enough for a proper refill.

5. 5

   Supply Line Kink or Fill Valve End-of-Life Failure

   A kinked flexible supply line or a very old fill valve can prevent any meaningful water flow into the tank. If the valve cap has already been cleaned and the shutoff is fully open, replacement is the normal next step.

Quick DIY Checks

1. 1Step 1 - Confirm the shutoff valve is fully open. Turn the valve behind the toilet counterclockwise until it stops, then flush and listen for refill. If the tank immediately starts filling, the issue was restricted supply.
2. 2Step 2 - Remove the tank lid and watch the float as you flush. Make sure the float cup or float arm drops freely and does not rub the tank wall, refill tube, or handle chain. If moving the float by hand starts the refill, the float or valve is sticking.
3. 3Step 3 - Clean the fill valve cap and inlet screen. Shut off the water, flush the tank, remove the cap from the top of the fill valve, and rinse out any grit or mineral buildup. Reassemble and test before buying parts.

Repair vs Replace

Recommended Tools & Parts

• Fluidmaster 400A Universal Fill Valve

  Common replacement fill valve for toilets that stop refilling after the flush or refill inconsistently.

  $10-$15

  Buy on Amazon →

• Braided Toilet Supply Line

  Flexible replacement supply line for toilets with kinked, corroded, or restricted water feed lines.

  $8-$15

  Buy on Amazon →

• Complete Toilet Tank Repair Kit

  Useful when the fill valve is worn and the flapper or other tank parts are also overdue for replacement.

  $18-$30

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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