Side-Entry vs Bottom-Entry Fill Valves: Which One Does Your Cistern Need?

A fill valve lets water into the cistern and shuts it off when the float rises. The job is the same on a side-entry valve and a bottom-entry valve. The hole is not. Side-entry water comes through the cistern wall. Bottom-entry water comes up through the base. If you order the other type, it will not fit the hole the hose is already using.

This is a selection guide for UK and European cisterns, where both types are common. It is not a full replacement procedure. Once you know which inlet you have, the fitting steps are in how to replace a toilet fill valve.

Bottom-entry fill valve with a float cup and a height-adjustment rod, shown as a product cut-out — Bottom-entry example: the shank points down through the base of the cistern, and the float cup rides on the body.

Compact bottom-entry fill valve with the float built into the body — Another bottom-entry example, with the float built into the body. Useful where the cistern is narrow.

How to tell which inlet you have

Leave the water on for this look, and do not loosen a nut yet.

Find the supply hose. It is the flexible pipe that feeds the cistern, not the flush pipe that leaves toward the pan.
If that hose rises into the underside of the cistern and the large nut is underneath, you have a bottom-entry valve.
If the hose meets the cistern on the side wall and the nut is outside that wall, you have a side-entry valve.
On a close-coupled toilet the hose is often hidden beside the pan. Follow it with a torch rather than guessing from the flush button.
On a concealed cistern, look through the flush-plate opening and trace the hose. The button style does not tell you the inlet.

Use the hole the hose is already on. A capped spare hole is not a reason to change type unless the cistern maker says that hole is meant to be opened.

What is different, in practice

	Side-entry	Bottom-entry
Where the water enters	A hole in the side wall	A hole in the base
Where the nut sits	Outside the wall, on a horizontal shank	Under the cistern, on a vertical shank
Float you often see	An arm that needs room to swing	A cup or box on the valve body
Where it shows up	Many older UK cisterns, and some other European cisterns	Close-coupled toilets in many markets, including a lot of European tanks
Swap it for the other type?	Not in the same hole	Not in the same hole

Older UK cisterns are often side-entry. Many newer close-coupled cisterns are bottom-entry. Both exist in Europe, so the country on the address is not the check. The hose is the check. European vs American toilet tank parts is the wider comparison, including why a part bought for one market may not match a cistern from another.

What to check before you buy

Match the cistern you are repairing. A shop label that says “universal” still has to pass these checks.

Inlet position. Side or bottom, taken from the hose, not from memory.
The shut-off. Close the isolator that feeds this cistern and confirm the flow actually stops. If that valve will not close, use the main stopcock before any later work. Do not start a replacement until you can shut the water off.
Space. Measure the old valve and the clear space around it: up to the lid, across to the flush valve, and the path the float travels. A valve that is too tall hits the lid. A float that rubs the flush valve, the wall, or the button linkage will not shut the water off cleanly.
The supply connection. The new valve has to join the hose you already have, or a replacement hose you are fitting at the same time. Read any marking on the old valve or the hose, or measure the thread. Do not assume one size for every UK or European cistern.
The rest of the cistern. If the water keeps running after the level looks right, the fill valve may not be the only worn part. Start with why a toilet keeps running. If the flush valve is worn as well, a kit can be simpler than two separate parts: see how to choose a toilet tank repair kit.

Product notes for fill valves are on the fill valve page. Specifications are confirmed when you ask. This page does not list a flow rate, a pressure range, or a service life, because those figures are not the same for every valve and every water supply.

What you cannot tell from the outside

The flush button, or the lack of one, does not choose the inlet. A lever cistern can be bottom-entry. A push-button cistern can be side-entry. Concealed cisterns are often tied to one manufacturer’s parts, and a generic valve may not pass through the opening even when the inlet direction looks right.

Thread adapters exist in the trade, but each extra joint is another place to leak. Prefer a valve and hose that match, and confirm the fit before you order a quantity.

After you have chosen

Fitting is the same idea for both types: water off, cistern emptied, old valve out, new washers seated, nut snug but not crushed, then the level set so the water stops before it spills into the overflow. The hand work differs because one shank is horizontal and the other is vertical. Follow the replacement guide for the sequence, including the side-entry notes.

Frequently asked questions

Can I put a bottom-entry valve in a side-entry cistern? Not in the side hole. The shank, the washer, and the nut are arranged for a different direction. Use a side-entry valve in a side hole, and a bottom-entry valve in a base hole.

Is side-entry only a UK part? No. It is common on older UK cisterns and it also appears elsewhere in Europe. Bottom-entry is widely used in Europe as well. Check the cistern in front of you.

Do I have to take the cistern off the wall? A like-for-like valve is usually changed with the cistern in place, once the water is off and the cistern is empty. Concealed cisterns are the awkward case: access is through the plate opening, and the part may be specific to that cistern.

The cistern hisses or fills slowly. Is that an entry-type problem? Usually it is debris, a worn seal, or a valve that no longer shuts, not the direction of the hole. Replacing it still means matching the inlet you have. The running-cistern guide above is the place to separate a fill-valve fault from a flush-valve leak.

Does the valve need a certification? Some markets require an approval for parts on the drinking-water supply. Ask which documents apply to the model you want. This guide does not claim that a valve is WRAS, CE, or otherwise certified.

For distributors

Merchants who cover the UK and Europe usually need both inlets on the shelf, because the cisterns in the field are mixed. The fill valve page describes the part. Wholesale questions, including minimum order and lead time, go through the distributor inquiry. We reply by email. Ask us which approvals a destination market expects. We confirm the documents for each model rather than listing them here.