You flush the toilet and nothing happens. The bowl drains but the tank does not refill, or it fills painfully slowly, leaving you unable to flush again. A toilet that will not fill with water is a common plumbing problem, and in most cases, the cause is something that can be diagnosed and often fixed without too much difficulty.
In this guide, we will explain how a toilet's fill mechanism works, the most common reasons a toilet stops filling, troubleshooting steps you can try, and when it is time to call a Licensed Master Plumber.
Understanding the basic mechanics helps you troubleshoot more effectively. When you flush, the flush valve at the bottom of the tank opens, releasing water into the bowl. As the tank empties, the float (a ball or cup device) drops with the water level. When the float reaches a low point, it triggers the fill valve to open, allowing fresh water to flow into the tank through the supply line. As the tank refills, the float rises. When it reaches the preset water level, the fill valve closes, stopping the flow of water. The entire cycle takes about 60 to 90 seconds.
If any part of this chain fails, the tank will not fill properly.
The fill valve is the most common culprit when a toilet will not fill. Over time, the internal seals and diaphragm inside the fill valve wear out, preventing it from opening fully or at all. Mineral deposits from NYC's water supply can also clog the valve's internal passages. A fill valve that makes a loud hissing, whining, or foghorn sound is typically failing and will soon stop working altogether.
If the float is set too low, the fill valve shuts off before the tank is full, resulting in weak flushes. If the float is stuck in the up position, the fill valve never opens because it thinks the tank is already full. Ball floats (the ball on a metal arm) can develop cracks that allow water inside, making them too heavy to float properly. Cup floats (a cylinder that rides up and down the fill valve shaft) can get stuck due to mineral buildup on the shaft.
The supply line is the flexible hose or rigid pipe that connects the shut-off valve on the wall to the fill valve on the toilet. If this line is kinked, clogged, or has a failing connection, it restricts water flow to the tank. Braided stainless steel supply lines are the most reliable. Old plastic or rubber supply lines can deteriorate, kink, or crack over time.
Every toilet should have a dedicated shut-off valve on the wall or floor near the toilet. If this valve is not fully open, or if it has seized in a partially closed position, the tank will fill slowly or not at all. After any plumbing work in the area, always verify that the toilet's shut-off valve has been reopened fully.
If the water pressure in your building is too low, the fill valve may not receive enough pressure to open properly. This is especially common in older NYC buildings with corroded galvanized pipes, or on the upper floors of tall buildings where water pressure naturally decreases. If other fixtures in the bathroom also have weak flow, low water pressure is likely the underlying cause. See our guide on low water pressure for more information.
Debris from the water supply, including sediment, rust particles, and mineral flakes, can lodge in the fill valve's inlet screen. This tiny filter is located where the supply line connects to the fill valve. A clogged inlet screen restricts water flow and can cause the tank to fill extremely slowly or not at all.
Start with the simplest fix. Locate the shut-off valve near the toilet and make sure it is fully open. Turn it counterclockwise (for a gate valve) or make sure the lever is parallel to the pipe (for a ball valve). If the valve was partially closed, opening it fully should restore flow.
Remove the tank lid and look at the float mechanism. If you have a ball float, check that the ball is not cracked and waterlogged. Check that the float arm moves freely and is not bent in a way that keeps the float too high. If you have a cup float, make sure it slides freely on the fill valve shaft. Clean any mineral buildup from the shaft with a damp cloth.
Most fill valves have an adjustment screw or clip that sets the water level. The water level in the tank should be about 1 inch below the top of the overflow tube. If the level is set too low, adjust it upward. Refer to the fill valve manufacturer's instructions for the specific adjustment method.
Turn off the water supply and flush the toilet to empty the tank. Disconnect the supply line from the fill valve and check the inlet screen for debris. Clean it if clogged. If the fill valve is old and has internal wear, replacement is the better option. Universal fill valves are inexpensive and available at any hardware store. Installation takes about 15 minutes.
Check the supply line for kinks, cracks, or corrosion. If the supply line is old or damaged, replace it with a new braided stainless steel line. Make sure the connections at both ends (wall valve and fill valve) are tight but not overtightened.
Sometimes a toilet that will not fill is a symptom of a larger problem:
Call a professional when:
Karl's Plumbing, Heating & Cooling has been handling residential plumbing repairs and installations across New York City for four generations. Our Licensed Master Plumbers (LMP #921 and LMP #2060) can quickly diagnose why your toilet is not filling and fix the problem, whether it is a simple fill valve replacement or a more involved piping issue.
Call us at (800) 721-3200 or (718) 263-8600. We service Manhattan, Brooklyn, Queens, the Bronx, Staten Island, Long Island, and Westchester.
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