Fluidmaster 400AC Installation Instructions Download Page 1

– Please keep a copy of these instructions on the property in which the product was installed.

If Replacing Seal: 

Use only a genuine 

Fluidmaster 242 seal.

Removing Valve Cap Assembly, Flushing Out Debris, Replacing Seal, & Replacing Valve Cap Assembly

SEAL

LOCATION

A

242

SEAL

B

Removing Valve Cap Assembly

Turn off water supply 

& flush out tank. Push 

float up with right hand 

(see picture). Grip and 

hold shaft under float 

with right hand. With left 

hand, twist cap and lever 

counter clockwise 1/8th 

of a turn to unlock the top 

cap. Pressing down on top 

may be helpful with older 

valves. Let cap assembly 

hang on float cup.

Replacing Valve Cap

A.  Place cap assembly on top of gray valve 

body by aligning cap arm and adjustment 

rod next to refill tube.
B.  Press down on top cap while rotating 

top & arm clockwise to locked position.

Flushing Out Debris

Hold cup upside down over 

uncapped valve to prevent 

splashing. Turn water supply 

on and off a few times. 

Turn water supply off when 

putting cap back on valve.

If Replacing 

Seal

IF FILL VALVE DOES NOT TURN ON, WILL NOT 

TURN OFF, OR WILL NOT REFILL THE TANK 

AFTER THE FLUSH

•  Remove top cap and check for debris. If you find debris, or flow 

is weak: Inspect lower section of fill valve for partial blockage. 

Partial blockage may be at shut off valve or in water supply line 

(See “REMOVING THE VALVE CAP ASSEMBLY & FLUSHING OUT 

DEBRIS”).

•  If fill valve has been in use for some time and/or float cup does not 

drop when flushing tank, replace seal with a genuine Fluidmaster 242 

seal (See “IF REPLACING SEAL”).

IF FILL VALVE TURNS ON AND OFF BY ITSELF

•  This indicates the tank is losing water. The fill valve is refilling lost water. 

Clean flapper and drain seat. If leak continues change flush valve. Install 

Fluidmaster 507AKR, 540AKR or 555C kit.

IF WATER LEVEL IN BOWL IS TOO LOW

•  Make sure the refill tube is supplying water down overflow pipe.
•  Water level in tank may be too low. Raise water level to 1/2” below top of 

overflow pipe (See “ADJUSTING TANK WATER LEVEL”). You may have 

to lengthen the fill valve in order to increase the water level in tank (See 

“PREPARING THE FILL VALVE FOR INSTALLATION”).

•  Flapper may be closing too soon. Give flapper chain approximately 1/2” 

of slack.

TR

OU

BL

ES

H

OO

TI

N

G

B

D

A

OVERFLOW

PIPE 

FILL 

VALVE 

C

WATER 

LEVEL 

6

Once fill valve is installed, ensure overflow pipe and 

water level of tank are correctly set.

1. THE TOP OF OVERFLOW PIPE (A) must be minimum of 1" 

below TANK LEVER HOLE (B).
2. WATER LEVEL (C) is set below top of Overflow Pipe 

(Fluidmaster recommends 1/2”).
3. THE CRITICAL LEVEL MARK / C.L. Mark (D) identified by 

C.L. on fill valve must be positioned 1” above top of overflow 

pipe. This is a requirement of the Universal Plumbing Code.

Code Compliance helps protect your home & drinking water 

supply.

Code Compliance

5

With water turned on, set float cup to desired level, by 

turning water level adjustment screw. When adjusting float cup, 

flush tank first. Then make adjustment while tank is filling.
To adjust tank water, turn adjustment screw clockwise to raise 

water level or counter clockwise to lower water level. Once 

adjusted, flush toilet and check new level. Repeat if necessary.
HINT: When you twist adjustment screw 8 times - float moves 1/2”.

Adjusting Tank Water Level

B

A

Inspect water supply connector. Replace it if it is worn or over 5 

years old to prevent flooding and property damage.
A. Attach water supply coupling nut to fill valve. Turn coupling nut 

clockwise by hand until tight. 
WARNING: Do not over tighten the nut as it could damage fill valve or 

coupling nut, resulting in flooding and property damage. Fluidmaster Click 

Seal

®

 connector is recommended: A perfect seal every time without over 

tightening.
B. Turn on water supply and check for leaks. If you find leaking at bottom of 

tank, turn nut just enough to stop leaking. Then flush toilet to check.

Attach Water Supply Connector

Correct set up of refill tube and refill clip to overflow pipe

REFILL

CLIP

REFILL TUBE

NIPPLE

3

Place fill valve in tank. Make sure lid will sit on top of tank without touching 

valve. Align fill valve nipple to face center of tank. Press down on shank from inside 

tank while tightening locknut. 
Hand-tighten only. DO NOT OVER TIGHTEN. Over tightening 

may crack the fill valve or tank causing flooding. Make sure the 

float cup does not touch the tank walls or tank lever and flush 

valve.
Attach one end of refill tube to refill clip. Place clip on right 

side of overflow pipe. Attach other end of tube to nipple on fill 

valve with a slight arch (See drawing to the right). Cut tube as 

necessary. 
WARNING: Do not shove refill tube down overflow pipe. This 

may cause significant water waste.

Installing New Fill Valve

IN

STA

LL

AT

IO

N

“C.L”

MARK

MEASURE

HEIGHT ONLY:

DO NOT INSTALL

LOCK

RING

1

Position fill valve in tank, but do not fully install yet. Top 

of fill valve MUST be set 3” above overflow pipe. This will 

automatically place CRITICAL LEVEL MARK / C.L. Mark

1” above the top of overflow pipe. Remove fill valve from 

tank to adjust height.
Adjust height of fill valve by holding lower shank with right 

hand and top of valve with left hand. Twist the lower shank 

counter clockwise to increase valve height and clockwise 

to decrease valve height. You should hear several “clicks”. 

Place valve in tank and check height again. THE CRITICAL 

LEVEL MARK, identified by C.L. on valve, MUST be 

positioned 1” above top of overflow pipe. This is a 

requirement of the Universal Plumbing Code.
Do not move lock ring.
 It holds the valve body and shank 

together under pressure. Do not interchange body with old 

shank as leaking can occur.

A

B

E

Shank

Washer

Threaded

Shank

Place shank 

washer onto 

threaded 

shank of fill 

valve. Flat 

side up.

D

C

2

Fill Valve Assembly Parts

A)  Refill Clip

B)  Refill Tube

C)  Shank Washer

D)  Locknut

E)  Threaded Shank

Preparing the Fill Valve for Installation

PR

EP

AR

AT

IO

N

1

Remove tank lid. Use pencil to mark water level of 

tank. Then follow steps A-C.
A. Turn off water supply (Clockwise). Flush toilet and remove 

excess water from tank with sponge.
B. Remove water supply coupling nut. Remove locknut from 

under tank.
C. Remove fill valve from tank.

Remove Old Fill Valve

A

B

C

PARTS

IN THIS KIT:

(1) Fill Valve
(1) Shank Washer
(1) Locknut
(1) Refill Tube
(1) Refill Clip

30800 Rancho Viejo Road, San Juan Capistrano, CA 92675

www.Fluidmaster.com  •  800-631-2011

Contact Fluidmaster for troubleshooting help or visit www.fluidmaster.com

M-F 5:30 am - 5:00 pm PST.

TOOLS

NEEDED

Scissors

Sponge

FLUSH

VALVE

OVERFLOW

PIPE

TANK LEVER

FLAPPER

FLOAT

CUP

LOCK RING

REFILL TUBE

FILL

VALVE

REFILL CLIP

TANK SHOULD 

LOOK LIKE THIS 

WHEN SET UP IS 

COMPLETE

SHANK

WASHER

LOCKNUT

DO NOT USE

DO NOT USE IN-TANK DROP-IN TOILET BOWL CLEANERS CONTAINING BLEACH OR 

CHLORINE.

 Use of such products will:

 (1) RESULT IN DAMAGE

 to tank components and 

MAY 

CAUSE FLOODING

 and 

PROPERTY DAMAGE

 and 

(2) VOID FLUIDMASTER WARRANTY.

Fluidmaster Flush 'n Sparkle Toilet Bowl Cleaning System

 is recommended for those 

choosing to use in-tank bowl cleaners and 

WILL NOT VOID

 the 

FLUIDMASTER WARRANTY

 

because it will not damage the components. 

DO NOT 

overtighten nuts or tank/bowl may crack. Always use quality 

Fluidmaster parts when installing or repairing. Fluidmaster will not be responsible or liable for use of non-Fluidmaster parts 

during installation or repair.

   WARNING

FLUIDMASTER

®

400AC FILL VALVE

INSTALLATION INSTRUCTIONS

LIMITED FIVE-YEAR EXPRESS WARRANTY

Subject to the “Exclusions” set forth below, Fluidmaster Inc. promises to the consumer to repair, or at the option of Fluidmaster Inc. to replace any 

part of this plumbing product which proves to be defective in workmanship or materials under normal use for five years from the date of purchase. All 

costs of removal, transportation and reinstallation to obtain warranty service shall be paid by the consumer. During this “Limited Five Year Express 

Warranty,” Fluidmaster Inc. will provide, subject to the “Exclusions” section set forth below, all replacement parts free of charge, necessary to correct 

such defects. This “Limited Five Year Warranty” is null and void if this plumbing product has not been installed and maintained in accordance with all 

written instructions accompanying the product, and if non-Fluidmaster Inc. parts are used in installation.

E

XCLUSIONS: 

FLUIDMASTER INC. SHALL NOT BE LIABLE FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES, INCLUDING COSTS OF INSTALLATION, WATER 

DAMAGE, PERSONAL INJURY OR FOR ANY DAMAGES RESULTING FROM ABUSE OR MISUSE OF THE PRODUCT, FROM OVERTIGHTENING OR FROM FAILURE 

TO INSTALL OR MAINTAIN THIS PLUMBING PRODUCT IN ACCORDANCE WITH THE WRITTEN INSTRUCTIONS, INCLUDING USE OF NON-FLUIDMASTER PARTS. 

DO NOT USE IN-TANK DROP-IN TOILET BOWL CLEANERS CONTAINING BLEACH OR CHLORINE. USE OF SUCH PRODUCTS WILL RESULT IN DAMAGE TO TANK 

COMPONENTS AND MAY CAUSE FLOODING AND PROPERTY DAMAGE. USE OF SUCH PRODUCTS WILL VOID THIS WARRANTY.

PART# 4-744, Grev. 4, 12/13

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