Ballvalves and Float Valves — Tank Replacement, Servicing, and Water Regulations Compliance

What Are Ballvalves and Float Valves?

Ballvalves (also called float valves or ball float valves) are automatic water control valves used to maintain a preset water level in a cistern, tank, or vessel. When the water level falls — for example, when a WC cistern is flushed — the float descends, opening the valve to admit water from the supply. As water refills the cistern, the float rises until it closes the valve at the desired level.

They are found throughout UK plumbing installations in:

• WC cisterns (close-coupled and low-level)
• Cold water storage cisterns (CWSCs) in the roof space
• Feed and expansion (F&E) tanks for vented central heating systems
• Industrial and agricultural storage tanks
• Livestock water troughs and irrigation systems

Despite their simple function, ballvalves are governed by the Water Supply (Water Fittings) Regulations 1999 and must be correctly specified to prevent contamination of the potable water supply.

Types of Ballvalve

Portsmouth-Type Ballvalve

The traditional Portsmouth valve uses a horizontal piston that moves back and forth as the float arm rises and falls. The seat faces the water supply inlet. Portsmouth valves have become largely obsolete in new installations because:

• They close against supply pressure, which causes water hammer in high-pressure installations
• The design creates a submerged inlet below the water line, posing a potential backflow (back-siphonage) risk
• They are not compliant with the Water Fittings Regulations in many applications without additional backflow protection

Portsmouth valves are still encountered in older cisterns and cold water storage tanks. On low-pressure (gravity-fed) systems below 0.5 bar, they remain functional. However, for any replacement or new installation work, modern diaphragm-type valves are strongly preferred.

Diaphragm-Type Ballvalve (BS 1212 Part 2 and Part 3)

Diaphragm valves use a rubber or elastomeric diaphragm pressed against the seat by the float arm. As the water level rises, the float arm pushes the diaphragm onto the seat to shut off flow. Advantages:

• The diaphragm seals against a smooth seat — resistant to scale and wear
• Quiet operation compared to Portsmouth valves (less water hammer)
• Suitable for higher supply pressures
• Available in high (HP), medium (MP), and low (LP) pressure variants for different system pressures

BS 1212 Part 2 covers brass-body diaphragm valves; Part 3 covers plastic-body diaphragm valves. Both must incorporate a high water level shut-off that prevents the outlet from becoming submerged — the outlet point must be a minimum of 25mm above the Warning Pipe level in a cold water storage cistern, or above the overflow pipe invert in a WC cistern.

Equilibrium Ballvalves

Standard ballvalves must work against supply pressure to close. On high-pressure supplies (above 3 bar), this requires a strong float arm or large float to generate sufficient closing force, and the closing action can cause water hammer. Equilibrium valves equalise supply pressure on both sides of the valve head, requiring only minimal force to close. They are preferred on mains-pressure supplies and commercial applications where water hammer is unacceptable.

Torbeck-Type Valves (Side-Entry and Bottom-Entry)

Torbeck and similar compact diaphragm valves are now standard in modern close-coupled WC cisterns. They are compact (fitting within the narrow cistern), operate on both mains pressure and reduced pressure, and fill quietly from a side or bottom inlet below the water line with an anti-siphon device (air gap) built in. Most Torbeck valves comply with Fluid Category 4 backflow protection via the integral air gap.

Water Regulations and Backflow Prevention

The Water Supply (Water Fittings) Regulations 1999 (England and Wales), Water Byelaws (Scotland), and equivalent regulations (Northern Ireland) all require that water fittings are installed to prevent contamination of the potable supply. For cisterns and ballvalves, the key requirement is backflow prevention appropriate to the fluid category risk.

Our dedicated backflow prevention guide covers the full fluid category system, but for cisterns the relevant categories are:

• Fluid Category 2: WC cisterns with domestic water not contaminated by faecal matter. Requires a minimum Type A air gap (BS EN 1717) or a device providing equivalent protection between the inlet and the cistern water level
• Fluid Category 3: Hot water systems, where water may be warm enough for bacterial growth. Requires a single-check valve as minimum
• Fluid Category 4: Cold water storage cisterns used for wholesome water supply that may be contaminated by chemicals or substances hazardous to health. Requires a Type A air gap — the inlet must discharge above the Fluid Category 4 level specified in the Regulations
• Fluid Category 5: Chemical treatment tanks, agricultural cisterns. Requires a Type AA (unrestricted) air gap — the supply must be entirely disconnected from the cistern above maximum water level

The inlet of a ballvalve should discharge water above the water line in the cistern — never below. The minimum air gap (distance between the lowest point of the inlet orifice and the maximum water level in the cistern) must comply with the relevant BS EN 1717 requirements for the appropriate fluid category. In practice, most Water Fitting Regulations-approved ballvalves incorporate the required air gap by design.

Cold Water Storage Cisterns (CWSCs)

Cold water storage cisterns in the roof space supply cold water to baths, hot water cylinders, and sometimes cold taps in older properties. The cistern is typically constructed from GRP (glass reinforced plastic) or polyethylene and may hold 100–450 litres depending on the property size.

Cistern Requirements (Water Regulations)

A CWSC must have:

• A cover (not airtight — to prevent pressure build-up, but screened against insects, vermin, and light)
• A screened overflow pipe (Warning Pipe) discharging outside the building at a visible point
• An inlet ballvalve set so the water level is at least 25mm below the overflow pipe invert
• A servicing valve on the mains inlet supply (to allow ballvalve maintenance without draining the whole system)
• Insulation (top, sides, and bottom — insulate above the cistern, leave the loft floor uninsulated below to allow warm air from the house to reach the cistern and prevent freezing)

Ballvalve Selection for CWSCs

CWSCs on a mains-pressure supply (typically 1.5–3 bar at the cistern) require:

• High-pressure (HP) or medium-pressure (MP) rated ballvalve — check the valve's pressure range matches the actual incoming pressure
• Inlet above the overflow (Warning Pipe) level — or a valve with a documented air gap complying with BS EN 1717
• WRAS-approved valve (Water Regulations Advisory Scheme — the approval mark confirms regulatory compliance)

For very high-pressure supplies (over 3 bar), either fit an equilibrium valve or reduce supply pressure to the cistern inlet with a pressure-reducing valve (PRV). Our water pressure guide explains PRV selection and sizing, and our guide to PRVs covers pressure relief for pressurised systems.

WC Cistern Ballvalves

Modern close-coupled WC cisterns use compact side-entry or bottom-entry valves (Torbeck type). The key selection criteria are:

• Inlet type: Side-entry (most common in UK) or bottom-entry (for concealed cisterns and some slimline designs)
• Water pressure rating: Check supply pressure at the cistern — most Torbeck valves cover 0.05 to 10 bar, but verify for low-pressure gravity systems
• Float arm length: Adjustable float arms allow the shutoff level to be set to match the cistern capacity and flush volume requirement (6/4 litre dual flush WCs require precise level setting)
• Inlet size: 15mm (standard domestic) is almost universal in UK WC cisterns

Setting the Water Level in a WC Cistern

The correct water level in a close-coupled WC cistern is typically marked with a line inside the cistern body or documented in the WC manufacturer's installation guide. Water should be 25–50mm below the overflow pipe invert. To adjust:

1. Adjust the float arm — on older Portsmouth valves, bend the arm slightly downward to lower the shutoff level; on modern diaphragm valves, turn the adjustment screw or slide the float position on the arm
2. Flush and observe — allow the cistern to refill fully and check the water stops at the correct level
3. Check there is no continuous drip through the overflow — if water trickles from the overflow pipe, the shutoff level is set too high or the valve diaphragm is worn

Feed and Expansion Tanks for Vented Heating Systems

Older vented central heating systems use a feed and expansion (F&E) cistern in the loft, typically a small (15–25 litre) tank that keeps the system topped up and accommodates thermal expansion of the water. The F&E tank operates on the same ballvalve principle as a CWSC but is much smaller.

The F&E tank ballvalve is normally set at a low water level — just enough to cover the feed pipe when the system is cold, allowing space for expansion when the system heats up. Common problems:

• Ballvalve stuck open: Continuous cold water entering the F&E tank indicates the system is losing water from a leak or through the overflow. The ballvalve may also be set too high, causing constant overflow
• F&E tank overflowing: Usually caused by a faulty or corroded expansion vessel or a balloon in the heating system that has burst — not a ballvalve fault. See our pressurisation and expansion vessel guide for sealed system diagnosis
• Ballvalve frozen: F&E tanks in poorly insulated lofts are susceptible to freezing in cold spells, blocking the water supply and causing the system to depressurise. Ensure the tank and feed pipe are insulated

Replacing a Ballvalve: Step-by-Step

Tools and Materials Required

• Replacement ballvalve (correct type and pressure rating)
• PTFE tape (for threaded connections)
• Adjustable spanner and slip-joint pliers
• Servicing valve key (if the inlet has a flat-head servicing valve)
• Bucket and towel (for minor spillage)
• New tank connector with backnut and washers (if replacing the bulkhead fitting)

Procedure

1. Isolate the supply: Close the servicing valve on the mains supply to the cistern. If there is no servicing valve, close the nearest stopcock as described in our guide to stopcocks and isolation valves
2. Flush the cistern: Empty as much water as possible by flushing (WC) or opening a draw-off tap (CWSC)
3. Remove the old valve: Undo the float arm (usually clips off or is held with a pin), then undo the back-nut securing the valve body to the cistern side. Remove the valve body and the old tank connector/washer
4. Fit the new tank connector: If replacing the bulkhead fitting, insert the new tank connector with rubber washer on the inside of the cistern wall and tighten the back-nut firmly but without over-tightening (which can crack plastic cisterns)
5. Fit the new valve body: Apply PTFE tape to the male thread of the supply pipe tail (or use the new valve's integral olive/washer). Thread the valve body into the tank connector and tighten with a spanner — hand tight then approximately one further quarter turn
6. Reattach the float arm and float
7. Open the supply and check for leaks: Slowly open the servicing valve and observe all connections while the cistern fills. Check for weeping at the valve body and tank connector
8. Set the water level: Adjust the float arm so the water shuts off at the correct level (25mm below overflow invert for CWSCs; manufacturer's marked level for WC cisterns)

Common Ballvalve Problems and Remedies

WRAS Approval and Regulations Compliance

All ballvalves used in UK domestic and commercial water supply systems must comply with the Water Supply (Water Fittings) Regulations 1999. WRAS (Water Regulations Advisory Scheme) approval provides evidence of compliance. When specifying a replacement valve:

• Check the WRAS approval certificate number on the product packaging or manufacturer's website
• Confirm the valve is rated for the actual supply pressure at the cistern — exceeding the rated pressure can cause leaks and premature failure
• For commercial or institutional work, keep records of the WRAS-approved fittings used in case of a Water Authority inspection

Water undertakers (Thames Water, Anglian Water, etc.) have the right to inspect water fittings and require rectification of non-compliant installations. Non-compliance with the Water Fittings Regulations is a criminal offence under the Water Industry Act 1991.

Summary: Ballvalve Selection and Maintenance

• Specify WRAS-approved diaphragm-type ballvalves for all new and replacement work — avoid Portsmouth-type valves
• Match the valve pressure rating (LP/MP/HP) to the actual supply pressure at the cistern
• Fit an equilibrium valve or PRV on supplies above 3 bar to prevent water hammer
• Ensure the valve inlet discharges above the cistern water line with the correct air gap for the fluid category risk
• Always install a servicing valve upstream of the cistern to allow future valve maintenance without shutting off the whole supply
• Set the water level 25mm below the overflow (Warning Pipe) invert on CWSCs
• Replace worn diaphragms on diaphragm valves before replacing the whole valve — rebuild kits extend valve life significantly in hard-water areas

Products from APM Plumbing & Electrical

APM Plumbing & Electrical stocks a range of float valves and ballvalves including BS 1212 Part 2 brass diaphragm valves and HP-rated float valves. These are currently available as trade counter and POS products — CM to confirm online catalogue publication status before adding product cards. Contact APM for trade pricing.

Related published products:

CM note: 1/2" Part 2 Ballvalve Brass, HP PT1 Float Valve, Peerless B/E Brass Tail Float Valve, and Delchem Side Float Valve are in the APM catalogue but not currently published to the online store. Publish and add product cards before the target date of 2028-04-30.

Visit us at APM Electricals, 31 Inglis Road, London, W5 3RL. Call 020 8819 5852.

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