Why does my toilet fill so slowly?

Fluidmaster, a major maker of fill valves, is direct about it. Its troubleshooting page says the main reason for a tank not filling or filling slowly is the toilet fill valve. It names two common reasons for the valve to slow down after a flush: debris issues and the length of time the valve has been in use.

Here is how that breaks down.

• Debris. Fluidmaster says debris that builds up over time inside the water system, including the valve body, the supply line or the shutoff valve at the wall, can restrict the flow path of water and slow the valve's filling speed.
• Age. Fluidmaster says fill valves in use for 7 years or more can have their working parts start to wear out.
• A shutoff that is not fully open. The City of Phoenix lists a partially closed house valve as a potential cause of reduced water pressure. The same logic applies to the small valve behind the toilet.
• Low water pressure. If the whole house has weak pressure, the toilet will refill slowly along with everything else.
• A worn or damaged supply line. Fluidmaster's 400A sheet tells you to inspect the water supply connector and to replace it if it is worn or over 5 years old.

Notice the pattern. Most causes sit between the street and the fill valve, so the fix starts at the wall and works toward the tank.

### Is it the toilet or the whole house?

Answer this before you touch a part. Run a nearby sink and a shower. If they are slow too, the problem is not the toilet.

The City of Phoenix says an acceptable pressure range within the city is between 40 and 100 psi, and that it does not regulate the pressure beyond the meter on the customer's side. The city also says fluctuations are normal and that everyone getting ready in the morning can lower pressure in the early hours. If pressure is consistently low, its page says the cause could be on the city's side or the customer's side, and that the city is responsible for issues between the street and the water meter while the homeowner is responsible after the meter.

Sinks give you a quick test, and the city's own list of causes points at them too: debris in aerator screens on bath and kitchen sinks. If only one faucet is weak, that aerator is a likely culprit, and our page on low pressure at one fixture covers it. If everything is weak, see low pressure in the whole house.

These two checks take a minute and need no tools. Do them first.

### Is the shutoff valve fully open?

The shutoff valve is the small valve on the wall or floor where the supply line meets the toilet. Turn it slowly counterclockwise until it stops. A valve that is only partly open will still fill the tank, but slowly. Fluidmaster's sheet notes that partial blockage may sit at the shutoff valve itself.

Turn it gently. If it feels stuck, or it drips at the stem when you move it, stop and leave it as is. An old valve that leaks when disturbed needs replacing, not forcing. See replacing a toilet shutoff valve for what that involves, and how to shut off water to a fixture if you are unsure which valve does what.

### Is the supply line kinked, worn or old?

Look at the line from the valve to the bottom of the tank. Check for a sharp bend, a flattened section, corrosion at the nuts, or damp spots. We did not find a manufacturer sheet that discusses kinks by name, so this is a visual check. What the Fluidmaster 400A sheet does say is to inspect the water supply connector and replace it if it is worn or over 5 years old, to prevent flooding and property damage.

If the line is old or damaged, replace it rather than trying to straighten it. Our page on replacing a toilet supply line shows the steps. Do not over-tighten the coupling nut. Fluidmaster warns that over-tightening could damage the fill valve or the nut and cause flooding.

This is the fix both Fluidmaster and Kohler point to first. Kohler's support page says flushing the fill valve on a Kohler two-piece toilet takes under 10 minutes, needs only a plastic cup, and may resolve a toilet that is running, noisy or not refilling.

Fluidmaster's steps for its valves with a removable top cap look like this. Your valve may be a different make, so follow the sheet that came with it if you have one.

1. 1Turn off the water supply at the shutoff valve, then flush the tank to empty it.
2. 2Lift the float cup. Reach inside, put your hand under the float cup, and lift it. Hold the gray shaft and keep the float cup all the way up. Do not let the float cup drop or the valve shaft turn.
3. 3Release the cap. With your other hand on top of the valve cap, turn the cap and lever counterclockwise 1/8th of a turn to release it. Lift off the cap and lever from the valve body.
4. 4Look for debris. Check the seal (the rubber disc with the pin through it) and the valve portion still in the tank.
5. 5Flush it out. Hold a cup upside down over the exposed opening so the water does not spray. Turn the water supply on full force for 10 to 15 seconds, so the pressure frees debris inside the valve inlet. Fluidmaster's 400A sheet words it as turning the supply on and off a few times.
6. 6Turn the water off, then put the cap back. Line up the cap arm next to the refill tube, press down, and turn the cap and arm clockwise to lock.
7. 7Turn the water back on and flush. Watch the refill.

That is the whole job. If the tank now refills at its old speed, you are done.

### What if the valve is jammed or the water sprays?

Turn the water off at the shutoff valve and start over. A cup held over the opening is there for a reason. If the top cap will not turn, or you are not sure which type of valve you have, stop. The Fluidmaster sheet says pressing down on top may help with older valves, but do not force it.

### Should you use in-tank bowl cleaners?

Fluidmaster's page warns against in-tank drop-in bowl cleaners containing bleach or chlorine. It says they will damage tank components, may cause flooding and property damage, and will void the warranty on Fluidmaster products. Follow the label on any cleaner you use. If you have such a tablet in the tank, that may be part of why the valve is failing.

If flushing debris does not help, Fluidmaster's next step is repair or replacement. Its 400A sheet says that if the fill valve has been in use for some time, or the float cup does not drop when the tank is flushed, you should replace the seal with a genuine Fluidmaster 242 seal. Fluidmaster's page also lists replacement top cap assemblies and complete valves.

Age is the tiebreaker. If your valve is well past the 7 years Fluidmaster mentions, a new one is a sound fix. For the job itself, see replacing the flapper and fill valve and adjusting a Fluidmaster fill valve.

Toilet makers also publish pressure needs for their products. One TOTO spec sheet we opened, for a Drake model, lists a minimum water pressure of 8 psi (flowing). That figure is for that one model only, so check the sheet for yours if you suspect a pressure issue.

### Does a slow fill mean a leak?

Sometimes the reverse is true, and the tank is refilling more often than you think. Fluidmaster's 400A sheet says that if the fill valve turns on and off by itself, the tank is losing water and the valve is refilling it, and it points to cleaning or changing the flapper and drain seat. The EPA says you can find a toilet leak by putting a few drops of food coloring in the tank. If any color shows up in the bowl after 10 minutes, you have a leak. The EPA says to flush right away afterward to avoid staining the tank.

If that test shows color, read how to fix a running toilet. If the tank fills fine but the bowl water level looks low, see why the toilet bowl water level is low.

### What about noise, pressure and other odd behavior?

A slow fill often comes with a hiss or whistle, because water is squeezing through a partly blocked valve. Our page on a noisy or whistling fill valve covers that. A toilet that refills without being flushed is a related problem, covered in why a toilet flushes on its own.

If your pressure is the issue, note what the numbers mean. EPA's WaterSense sheet says it recommends incoming service pressure between 45 and 60 psi, and says most U.S. plumbing codes require pressure-regulating valves where supplied pressure exceeds 80 psi. Our page on what home water pressure should be explains how to read a gauge. Do not adjust a pressure regulator without knowing what you are doing. A wrong setting can damage fixtures.

Call if the shutoff valve will not turn or leaks when you touch it, if the supply line is corroded or damp, if flushing and a new valve do not fix the slow fill, or if pressure is weak at every fixture and the city's side is not the cause. Those problems live in the valves and pipes in the wall, and they are worth handling with the right parts and a proper shutoff.

HQ Plumbing & Air is licensed and insured, gives free estimates and quotes an upfront price before work starts. If water is leaking near the toilet and you cannot stop it, we offer 24/7 emergency service. See our residential plumbing services.