The first thing you need to do is lift off the tank lid and look inside the tank at the fill valve that is there. You need to look at it and make sure that the Fluidmaster 400A will fit in your toilet. The height is adjustable from 9” to 14” and it has a small diameter that usually does not conflict with other parts in the tank. There are some toilets that have proprietary fill valves that mount in the corner of the tank, incorporate parts of the flush valve with the fill valve, and some like the Toto G-Max have a special fill valve that has a higher bowl refill rate. Take a look at the two pictures below showing different fill valves to see how they compare with yours and see if the Fluidmaster 400A is compatible with your toilet. If you have a fill valve that is very complicated that usually goes along with expensive and I would seek the advice of a plumber. Some of the valves pictured below in the second picture down are in the $400 price range. A knowledgeable plumber may be able to rebuild them if parts are available.

Common Fill Valves

Most fill valves are quite common resembling the ones in the picture to the right which can be clicked on to enlarge. These fill valves or, ballcocks as we call them in the trade are stand alone devices and not tied to other components in the tank. The tank mounting hole is far enough out of the corner of the tank where the Fluidmaster 400A can be installed without interference from the tank or, other components. In some cases The Fluidmaster 400A will work with low profile toilets but in other cases the valve height cannot be adjusted low enough or the operational range is insufficient in which case a proprietary fill valve would be required.

Proprietary Fill Valves

On a few toilets there are designs which require the use of a special fill valve. Sometimes it is a low profile tank where the Fluidmaster 400A cannot be adjusted low enough or, be set to turn on and off in the right range. Other times the manufacturer just puts the hole in the tank to close to a corner or side so the float will hit against the tank not having the clearance it needs to operate. Sometimes they also have unusual tubes that flow water to the bowl at different times triggered by the water level in the tank or, different bowl water level replenishment rates. Many of the possible fill valves that would not be able to be replaced by a Fluidmaster 400A fill valve are pictured to the left in the picture which you can click on to enlarge.

How To Change A Fill Valve Step By Step

The following steps should be followed to replace the fill valve:

1.)    Shut of the angle stop valve supplying the toilet. This is usually located under the tank on the left side where the supply comes out of the wall or, floor. Flush the toilet and hold the lever so the tank empties as much as possible. Open the tank lid and place it on the floor out of the way. Placing it on the floor ensures it does not fall and break. Tank lids can be quite expensive. Remove the rest of the water from the tank using a sponge, wet vac, or, just be ready to catch the rest of the water with a bucket when the fill valve nut is loosened. Verify that the water is off completely.

2.)    Place a small tray to catch water under the angle stop valve if it comes out of the wall or, if it comes through the floor place rags around the pipe. Using a small adjustable wrench unscrew the nut on the supply line securing it to the angle stop valve. Then using channel lock pliers remove the nut securing the supply line to the old fill valve shank. A small amount of water will come out during this process.

3.)    You are now ready to remove the nut on the old fill valve shank. This is what secures the old fill valve in place. Use channel locks to loosen it. If you have removed all the water nothing will leak but if you haven’t you will need to get a bucket in place to catch the water that is remaining in the tank. Once the nut is removed the old fill valve will lift out of the tank. Unclip the bowl refill tube from the overflow tube and discard the whole assembly.

4.)    Remove the new fill valve and parts from the box. Cut the cone washer from inside of the shank washer. Place the shank washer on the fill valve shank with the smooth side facing up, the bottom of the shank washer has a ridge near the threads that helps the valve line up properly to the hole through the tank.

5.)    Place the new fill valve in the tank to check its height. Look at the picture to the right which you may click on to enlarge and note the critical level mark on the ring of the valve. This ring must be at least 1” above the overflow tube for the valve to work properly. The proper operation of the anti siphon valve depends on this height to protect your drinking water from the toilet tank back-flowing into it. The valve body has 2 pieces that adjust the height by screwing the bottom shank while holding the top of the valve body still. Once the height is correct place the refill tube on the fill valve then place the valve in the tank in a manner that does not conflict with the other parts in the tank and the refill tube points towards the overflow tube. Secure the fill valve in place with the nut provided. Do not over tighten as the tank and or, plastic shank of the fill valve can crack and leak. Make sure that the float does not hit the walls of the tank or the trip lever.

6.)    I recommend using a braided stainless steel supply line of the proper length to connect the water supply. They come in 9”, 12”, & 16” lengths. It is better to have one that is too long and loops rather than have it strained or, kinked. I do not recommend using the Watts Floodsafe closet connectors as I have seen some issues with them. I have seen them false trip and shut off the water supply to the toilet. But far worse I have seen a few that blew apart and caused a tremendous amount of water damage to the home. The connections on the braided stainless steel supplies are rubber gasketed and no Teflon tape or thread sealant is needed.

7.)    At this point remove the cap of the overflow tube if there is one present. Insert the refill tube into the overflow tube and hold it in place with your right hand. While holding the overflow reach down with your left hand and turn on the water supply at the angle stop valve. The tank should fill to the water line marked on the tank or, overflow tube or, if there is no mark to 5/8” below the top of the overflow tube. Turn the water level adjustment screw until the water level is set properly. If the float hits the stops on the adjustment screw without the water level at the correct height the height of the valve is wrong. At this point the valve can no longer be turned to adjust height, so a different method is used. Turn the water back off at the angle stop valve. Pull the locking collar up towards the float. This releases the screw so the valve can be raised or lowered by pushing and pulling. When the correct height is reached push the locking collar back down to again secure the valve in place. Failure to do this will cause the top half of the valve to launch and a resulting geyser. Make sure the collar goes all the way back down into the locked position.

8.)    Once the water level is set correctly pull the refill tube back out of the overflow tube. There are 2 ways to secure the refill tube to the overflow tube. The refill tube must fasten above the overflow tube and direct its flow into the tube. If the refill tube is down inside the overflow tube the water from the tank may siphon into the bowl causing the tank to keep refilling only to leak into the bowl again. The refill tube angle adapter can be used if there is room for the refill tube to feed it without stress or, kinking. Quite often I use the other method which is to remove the metal mounting clip from the angle adapter. The tube then goes over the round part of the metal clip and the clip secures to the overflow in the same manner. Trim the refill tube so it runs nicely without kinks of excessive loops.

9.)    Check for leaks and proper flush. Place the lid back on the tank and cleanup!

As you can see this job is not difficult in most cases and if the fill valve was not shutting off can often save you hundreds of dollars on your water bill.

The first thing to check is inside the tank. Remove the tank lid and set it on the floor. Tank lids can break easily and be hard to replace especially on older toilets putting the lid on the floor makes sure that it will not fall and break. Make sure the water level in the tank is at the proper level. It should be either to the water line marked on the tank, 5/8″ below the top of the overflow tube or, the line on the overflow tube. If the water is spilling over the top of the overflow tube, stop right now as you have found a big leak. Try adjusting the ballcock (fill valve) so the water level is maintained at the proper level. If the ballcock does not properly maintain the water level in the tank after being adjusted then it will need to be replaced. This is the silent leak that uses huge amounts of water.

The next two problems discussed usually result in what us plumbers call a ghost flush where you periodically hear the ballcock turn on and refill the tank even though no one has used the toilet. These are probably less dangerous in terms of wasting water because someone will hear the noise and usually take action to repair the problem.

The next thing to check is the tube that runs from the ballcock to the overflow tube. This tube is what refills the bowl with water after flushing. If this is shoved down into the overflow tube too far where it ends up being below the water level of the tank it will siphon water from the tank into the bowl where it then goes down the drain.

There are dye tablets available to test toilets. These are frequently available at plumbing supply houses, hardware stores, and Home centers. However, they are not required for the dye test as food coloring may be used. Put either the dye tablet or, food coloring into the tank. Do not flush the toilet! Wait 15 minutes then check back and see if the water in the bowl of the toilet has changed color. If the water has changed color the flapper should be replaced, then the toilet retested with the dye. In most cases the flapper replacement should fix the problem. Some times it may also be a case of the flapper chain being too tight or, a trip lever moving causing the chain to become tight as the lever moves.