Float Valves & Fill Valves — Bottom Entry, Side Entry and Brass for UK Plumbers

Whether you're servicing a noisy cistern, replacing a worn-out ballcock, or fitting a new toilet suite, a reliable float valve keeps water at the correct level and shuts off cleanly when the tank is full. This guide covers the float valves and fill valves stocked at APM Electricals — from Fluidmaster's modern fill valves to traditional brass-tail options — so you can pick the right part for the job.

What Is a Float Valve?

A float valve (also called a ballcock, fill valve, or cistern inlet valve) controls the flow of water into a toilet cistern or cold water storage tank. As water drains during a flush, the float drops and opens the valve to refill. Once the water reaches the set level, the float rises and closes the valve. A faulty float valve causes running toilets, slow fills, or overflow — one of the most common UK plumbing call-outs.

Bottom Entry vs Side Entry — What's the Difference?

• Bottom entry fill valves connect through the base of the cistern. Water enters from below, making them quieter and suited to most modern close-coupled and concealed cisterns.
• Side entry float valves connect through the side wall of the cistern. Common in older high-level, low-level, and some wall-hung cisterns. Also widely used in cold water storage tanks in loft spaces.
• Brass-tail float valves (Part 1/Part 2 pattern) are traditional valves fitted with a brass shank. Still specified on many commercial, agricultural, and older domestic jobs where robustness is essential.

Key Buying Points

Water pressure rating: Most domestic cisterns operate at low to medium pressure (LP or MP). Check your supply pressure if the cistern fills very slowly or the valve chitters on shut-off. High-pressure (HP) valves suit cold mains supplies fed directly from the rising main.

Adjustable arm length: A telescopic or adjustable arm lets you set the water shut-off level to match the cistern depth without cutting a rigid float arm.

Seismic/anti-siphon compliance: Modern Fluidmaster fill valves include an anti-siphon device as standard, meeting WRAS Water Fittings Regulations for connection directly to the mains.

Compatibility: Fluidmaster and Siamp valves are near-universal replacements for failed or noisy traditional ballcocks in close-coupled suites. Traditional brass Part 1/Part 2 valves suit storage tanks and older cisterns where float-arm geometry must be maintained.

Float Valves & Fill Valves at APM Electricals

Fluidmaster PRO400UK Pro Bottom Entry Fill Valve

Universal bottom-entry fill valve with ½″ shank. Quiet refill, adjustable height 15–23cm, suitable for most close-coupled cisterns.

£20.38

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Fluidmaster Airgap 6000 Side Entry Fill Valve

Brass and plastic side-entry fill valve with ½″ shank. Suits older cisterns and cold water storage tanks. WRAS-compliant anti-siphon device included.

£21.62

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Siamp 1/2″ BSP 99T Telescopic Bottom Inlet Float Valve

Siamp's telescopic bottom inlet valve for close-coupled cisterns. Extends to suit varying cistern heights. Popular direct replacement.

£18.99

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½″ Peerless B/E Brass Tail Plastic Float Valve Adj 7″–10″

Traditional bottom-entry float valve with brass tail and adjustable plastic float arm 7–10 inches. Suits storage tanks and older cisterns.

£8.99

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How to Replace a Float Valve in a Close-Coupled Cistern

1. Isolate the supply. Turn off the isolating valve on the cold supply pipe under the cistern (or the stopcock if there's no isolator). Flush to empty the cistern.
2. Disconnect the existing valve. Undo the locking nut under the cistern and the flex hose or supply pipe. Old plastic washer-type valves may need grips to unscrew the shank nut.
3. Remove the float arm. Traditional side-entry valves have a brass float arm clipped to the spindle. Fluidmaster-style valves are self-contained — just unscrew and lift out.
4. Fit the new valve. Insert the new valve through the cistern inlet hole (bottom or side, as appropriate). Hand-tighten the back-nut below the cistern, then firm up with a spanner — don't overtighten on plastic.
5. Reconnect the supply. Reattach the flex hose or pipe. Slowly open the isolating valve and check for leaks at both the valve shank and supply connection.
6. Set the water level. Turn the adjustment screw or slide the telescopic tube until the water cuts off approximately 25mm below the cistern overflow.
7. Test a full flush cycle. Confirm the valve opens quickly on flush and closes cleanly without running on.

Common Float Valve Faults and Fixes

Cistern running/not filling: Most often a worn diaphragm washer inside the valve seat. Replaceable without removing the whole valve — just unscrew the cap and swap the washer. If the valve body is cracked or corroded, replace the whole valve.

Slow fill: May indicate low mains pressure, a partially closed stopcock, or a clogged filter screen inside the valve inlet. Remove and rinse the filter under clean water.

Chattering or noise on shut-off: Water hammer from fast-closing valves. Fluidmaster valves close slowly by design. On older valves, a worn float arm pivot or loose float ball can cause vibration.

Water above overflow level: Float arm set too high, or float ball punctured (taking on water). Adjust the arm or replace the ball. On modern Fluidmaster fill valves, turn the adjustment screw anti-clockwise to lower the water level.

Float Valves for Cold Water Storage Tanks

Loft storage tanks typically use ½″ or ¾″ BS1212 Part 1 or Part 2 pattern valves with a brass shank and traditional float ball on an arm. These are rated for mains pressure and sized to fill large tanks efficiently. The Peerless brass-tail valve above is a direct replacement for this application. Ensure the float ball doesn't catch on the tank sides as the water level rises — use a 5–6 inch ball for standard domestic cold water tanks.

Shop Float Valves at APM Electricals

APM Electricals stocks a wide range of float valves, fill valves, float ball arms, and cistern fittings for trade plumbers and DIY. All orders placed before 3pm (Mon–Fri) ship same day on standard delivery. Browse the full range of cistern and float valve parts at APM Electricals.