Buy a Fluidmaster 400A when the fill valve itself is the problem. That means it won’t turn on, won’t shut off, refills the tank slowly even with the shutoff fully open, or leaks from the valve. The 400A is an adjustable-height replacement for many toilet tanks. It won’t fix a leaking flapper.

This page uses Fluidmaster’s product information and 400A installation guide. Nobody installed the valve for it.

Diagnose before buying

Turn off the stop valve and look at the tank. Then work through these:

  • Toilet runs or refills by itself: put a few drops of food coloring in the tank and wait without flushing. If color shows up in the bowl, water is leaking past the flapper or flush-valve seat. Fluidmaster’s own troubleshooting says a fill valve that turns on and off by itself means the tank is losing water. Clean or replace the flapper first.
  • Water runs into the overflow pipe: the fill valve isn’t shutting off, or the water level is set too high.
  • Slow fill: make sure the stop valve is fully open and the supply line isn’t kinked. Then check for debris in the valve. Fluidmaster’s guide shows how to remove the cap and flush debris out before you replace anything.

The diagnosis guide for running toilets goes through these checks step by step.

Compatibility

Fluidmaster calls the 400A universal, but your tank still has to fit it. It needs a bottom-entry inlet, room for the float to move, and clearance under the lid at the height you set. Specialty, concealed-tank, pressure-assisted and some low-profile toilets may need the maker’s own valve. Compare your current valve with the toilet manufacturer’s parts list if you’re unsure.

Installation settings from Fluidmaster’s guide

  1. Shut off and drain: turn off the water, flush, and sponge out what’s left in the tank.
  2. Set the height: twist the valve body so the top of the cap sits about 3 inches above the top of the overflow pipe.
  3. Install: put the shank washer on wide side up, connect the refill tube to the refill port, clip the refill clip to the overflow pipe, and tighten the locknut under the tank. If the refill tube is too long, cut it so it stays in the clip on the overflow pipe.
  4. Connect and check: attach the supply connector, turn the water on, and check for leaks.
  5. Set the water level: after it fills, the water should sit about 1/2 inch below the top of the overflow pipe. Turn the adjustment screw clockwise to raise it and counterclockwise to lower it.

Fluidmaster warns that overtightening nuts can crack the tank or bowl. It also warns that in-tank drop-in cleaners containing bleach or chlorine damage tank parts and void the warranty. If the float won’t drop after flushing, the guide says to replace the valve seal with a Fluidmaster 242 seal. If bowl water is low, give the flapper chain about 1/2 inch of slack.

Warranty

The 400A carries Fluidmaster’s limited five-year warranty, with exclusions listed on the back page of the instructions.

Verdict

The 400A is a practical repair for a fill valve that has actually failed in a standard tank. Rule out the flapper, the supply line and the shutoff first, then set the cap height and water level exactly as the instructions specify.

Sources