How to Replace a Toilet Fill Valve (Bottom-Entry and Side-Entry)

If your toilet tank won’t stop filling, refills very slowly, hisses, or the float no longer shuts the water off, the fill valve is usually the part to replace. It is one of the easiest plumbing repairs you can do yourself, and the replacement part is inexpensive and widely available.

This guide covers both main styles: bottom-entry valves (water comes up through the floor of the tank, common in North America, Latin America and many European close-coupled toilets) and side-entry valves (water enters through the side wall of the cistern, common in older UK and some European cisterns). If you are still choosing, read side-entry vs bottom-entry fill valves first.

Before you buy: identify your valve

Take a photo of the old valve before you go shopping, and check these four things:

1. Entry position: bottom or side.
2. Thread / connection size: In North America and much of Latin America, toilet supply connections are commonly 7/8” ballcock thread. In the UK and much of Europe, ½” BSP (G½) is common, and some European cisterns use ⅜”. Check the old valve or the existing supply hose rather than assuming.
3. Height range: Most universal valves adjust in height. Measure from the tank floor to the top of the overflow pipe and make sure the new valve’s range fits.
4. Tank space: Compact or concealed cisterns may not have room for a tall valve or a large float.

If you are in doubt, a “universal” adjustable fill valve fits many tanks, but not all. Concealed (in-wall) cisterns often need the manufacturer’s specific part.

Tools and materials

• New fill valve (with its washer and lock nut)
• Adjustable wrench or large slip-joint pliers
• Sponge and towel or a small bucket
• New flexible supply hose (recommended if the old one is old, kinked or corroded)
• Optional: torch/flashlight, gloves

Safety notes

• Turn off the water at the shut-off valve behind the toilet (usually clockwise, or a quarter turn on lever-type isolators). If it won’t close, use the main stopcock.
• Have a towel on the floor. There will always be some water left in the tank and the hose.
• Do not over-tighten plastic nuts. Over-tightening can crack the valve shank or the ceramic tank and cause a leak later. Hand-tight plus a small extra turn is usually enough, and the manufacturer’s instructions take priority.

Step-by-step: replacing a bottom-entry fill valve

Step 1: Shut off and drain

Close the shut-off valve, then flush and hold the lever or button to empty as much water as possible. Soak up the rest with a sponge.

Step 2: Disconnect the supply hose

Put a towel or bowl under the tank. Unscrew the supply hose nut where it connects to the bottom of the fill valve. A little water will come out.

Step 3: Remove the lock nut and old valve

Under the tank, unscrew the large plastic lock nut that holds the fill valve. Hold the valve body inside the tank so it doesn’t spin. Disconnect the refill tube from the overflow pipe (if there is one), then lift the old valve out.

Step 4: Clean the hole

Wipe the area around the tank hole. Remove any old washer residue or scale, because the new washer needs a clean, smooth surface to seal.

Step 5: Adjust the new valve height

Most universal valves adjust by twisting the shaft or by a locking collar. Set the height according to the instructions. Usually, the top of the valve or a marked critical level line must sit a set distance above the overflow pipe. This matters because anti-siphon protection only works when the valve is set at the correct height.

Step 6: Fit the new valve

Make sure the sealing washer is on the shank inside the tank, with the cone or flat side facing the way the instructions show. Insert the valve through the hole, then hand-tighten the lock nut underneath. Check that the float can move freely and won’t touch the flush valve, lever or tank wall.

Step 7: Reconnect the supply

Screw the supply hose back on by hand, then give it a small extra turn if needed. If your old hose is worn or older than the manufacturer recommends, replace it now. Many valve makers recommend this.

Step 8: Attach the refill tube

Clip the refill tube so it discharges into the top of the overflow pipe, held above the water line. Don’t push it deep into the pipe.

Step 9: Turn on and test

Open the shut-off valve slowly. Watch for drips at the lock nut and the hose connection. If you see a drip, turn off the water and tighten a little more, but don’t overdo it. Let the tank fill and check where the water stops.

Step 10: Set the water level

Adjust the float until the water stops at the tank’s marked water line, or roughly 1–2.5 cm below the top of the overflow pipe. See how to adjust the toilet water level for details.

Side-entry valves: what’s different

Side-entry valves are fitted through a hole in the cistern side wall, with a washer on each side and a back nut outside. The supply connects horizontally. The float is usually on an arm, and the level is set by an adjusting screw or by moving the float along the arm. The basic process is the same: water off, drain, disconnect, remove back nut, fit new valve with washers, reconnect, test, set level. Make sure the outlet points down into the cistern and the float arm has clear space.

Common problems after replacement

Problem	What to check
Drip under the tank	Washer seated? Nut snug? Hose connection tight?
Tank fills very slowly	Shut-off valve fully open? Debris in the valve?
Water runs into overflow	Float set too high, or valve not sealing
Noisy filling	Very high mains pressure. Some valves offer a flow restrictor; check the instructions
Float sticks	Float touching flush valve, chain or tank wall

Frequently asked questions

How long does a fill valve last? It depends on water quality, pressure and the valve design. Hard water and debris shorten its life. There’s no single figure that applies to every valve.

Can I replace a float-ball valve with a modern float-cup valve? Often yes, if the connection size and height fit. Float-cup valves take up less space and are easier to adjust.

Do I need to remove the tank? No. Fill valves can be replaced with the tank in place.

Is a universal fill valve really universal? “Universal” means it fits many common tanks. It doesn’t fit every tank. Check thread size, height range and space, especially for concealed or compact cisterns.

Does my fill valve need a certification? In many countries, parts connected to drinking water must meet local regulations (for example WRAS in the UK or ACS in France). Ask your supplier for documents for the specific product.

For distributors

Fill valves are a high-turnover replacement part for hardware stores, plumbing merchants and online sellers. We supply bottom-entry and side-entry fill valves and complete repair kits for European and Latin American markets, with private-label packaging available. Visit our For Distributors page to request a catalogue or send a wholesale/OEM inquiry. For the certification requirements of your market, please ask us to confirm what is available for each model.