Leatmere

Leatmere

UK home plumbing glossary

Plain-English definitions of common UK home plumbing, drainage and heating-water terms, with links to the relevant Leatmere guides.

Illustration of a stop tap, copper pipe, water droplet, radiator valve and reference cards.

A

Air admittance valve (AAV)

A one-way valve that lets air into a drainage system to help waste water flow without allowing foul air back into the room. See soil stacks and air admittance valves.

Airlock

A pocket of air that obstructs water circulation or flow in a pipe. It is different from trapped air at the top of a radiator. See airlocks in home plumbing.

B

Backflow

Water moving in the opposite direction to its intended flow, with a risk that contaminated water could enter the wholesome supply. See check valves and backflow protection.

Ball valve

A valve controlled by a float, used to stop a cistern filling when the water reaches its set level. Modern versions may use a compact float rather than a ball on an arm. See toilet fill and flush valves.

C

Check valve

A valve designed to allow flow in one direction only. The backflow protection needed depends on the water's contamination risk. See check valves and backflow.

Cold water storage cistern

A usually lidded tank that stores cold water, often in a loft, and supplies some outlets or a vented hot-water system by gravity. See loft cold-water tanks.

Combination boiler (combi)

A boiler that provides central heating and heats mains water on demand, normally without a separate hot-water cylinder. Any work on the gas boiler itself is for a Gas Safe registered engineer. See combi, system and regular boilers.

Compression fitting

A pipe joint in which a nut compresses an olive around the pipe to make a seal. See push-fit, compression and soldered joints.

D

Dead leg

A pipe leading to an outlet that is unused or rarely used, so water can remain still in it. HSE advises keeping hot water hot, cold water cold and water moving.

Double check valve

Two check-valve mechanisms in one body, used for certain backflow risks. An outside tap may need additional protection depending on how its hose is used; ask the water undertaker. See outdoor tap kits.

E

Expansion vessel

A sealed vessel containing a flexible diaphragm and an air or gas charge, allowing heated water to expand without an excessive pressure rise. See expansion vessels.

F

Flow rate

The volume of water delivered in a given time, usually expressed in litres per minute. It is not the same as pressure. See water pressure testing.

Foul water

Waste water from toilets, bidets, food preparation, cooking or washing. Approved Document H sets out the drainage arrangements for foul water in England.

G

Gate valve

A multi-turn valve that raises or lowers an internal gate. It is generally used for isolation rather than precise flow control. See gate valves and lever valves.

Gravity-fed system

A system in which stored water flows because the source is above the outlet. The vertical height between the stored-water level and outlet affects the available head. See shower-pump sizing.

H

A way of expressing water pressure as the height of a water column. WaterSafe notes that 10 metres of head is approximately one bar.

Heating inhibitor

A chemical added to a closed wet central-heating circuit to help limit corrosion and scale. It is not drinking-water treatment. See heating inhibitor and sludge.

I

Isolation valve

A local shut-off valve serving one fitting or appliance, so that it can be isolated without turning off the whole building's supply. See isolation valves.

J

Jumper

The moving washer carrier inside some traditional stop taps. WaterSafe lists a loose jumper as one possible cause of banging pipework.

K

Kitchen cold tap

The cold tap at the kitchen sink is normally supplied directly from the mains and is the tap DWI recommends for drinking and cooking.

L

Lockshield valve

The capped radiator valve used to restrict flow during system balancing. It is normally adjusted as part of balancing rather than everyday room-temperature control. See radiator bleeding and balancing.

M

Mains water

Water supplied by a water company through its distribution network, rather than from a private supply or a storage cistern within the home.

N

Negative-head shower pump

A pump intended for a gravity system where natural flow is too weak to trigger an ordinary positive-head pump. The pump maker's instructions and installer measurements decide suitability. See shower pumps compared.

O

Overflow pipe

A warning pipe or outlet that carries water away when a cistern continues filling above its intended level. A running overflow needs investigation rather than plugging. See overflow pipes.

P

Pressure-reducing valve (PRV)

A valve that reduces a higher inlet pressure to a controlled downstream pressure. Partly closing a stop tap restricts flow but is not a substitute for pressure control. See pressure-reducing valves.

PTFE tape

A thin thread-sealing tape used on suitable threaded joints. It is not a general-purpose repair wrap for leaking pipes. See PTFE tape.

Push-fit fitting

A pipe fitting that seals around an inserted pipe using an internal seal and retaining mechanism. Correct pipe preparation and the maker's instructions matter. See push-fit, compression and soldered joints.

Q

Quarter-turn valve

A valve that moves between open and closed through a 90-degree turn, commonly with a lever or screwdriver slot. See isolation valves.

R

Radiator bleed valve

A small valve near the top of a radiator used to release trapped air. The heating should be off and cool before it is opened. See radiator bleeding and balancing.

S

Soil stack

The main vertical drainage pipe that receives toilet and other foul-water discharges and connects them to the underground drainage system. See soil stacks and air admittance valves.

Stop tap (stopcock)

A valve that isolates the incoming water supply. The internal stop tap is often under the kitchen sink; the external one is commonly near the property boundary. See stopcocks and water meters.

T

Thermostatic mixing valve (TMV)

A valve that blends hot and cold water to limit the outlet temperature where there is a scalding risk. See thermostatic mixing valves.

Thermostatic radiator valve (TRV)

A radiator valve that changes the flow of heating water in response to room temperature. Its numbered settings are not identical temperatures across every model. See radiator valves and TRVs.

Trap

A shaped section beneath a basin, sink, bath or shower that retains a water seal to stop foul air entering the room. See basin wastes and bottle traps.

U

Unvented hot-water cylinder

A mains-pressure hot-water storage vessel with safety devices and a controlled discharge route. Installation and safety-device work belong to a competent person. See unvented cylinder basics.

V

Vented hot-water cylinder

A hot-water storage vessel with an open vent pipe and usually a cold-water storage cistern supplying it. See hot-water cylinders and immersions.

W

Water hammer

A pressure shock caused by a sudden change in water flow, often heard as banging. Loose pipes, fast-closing appliance valves or high pressure may contribute. See noisy pipes and water hammer.

Wholesome water

Water that meets the legal quality requirements for drinking and food preparation. Approved Document G uses the term for supplies to drinking-water outlets and kitchen sinks.

X

Cross-linked polyethylene (PEX)

A flexible plastic pipe material made from cross-linked polyethylene. Use only pipe and fittings suitable for the intended water service and follow the manufacturer's jointing system. See copper and plastic pipe types.

Y

Y-strainer

A Y-shaped fitting containing a removable screen that catches debris before it reaches a valve or appliance. Service it only after the relevant water circuit has been safely isolated.

Z

Zone valve

An electrically operated valve that directs heating water to a particular circuit, such as radiators or a hot-water cylinder coil. Electrical diagnosis and any work inside a gas boiler belong to qualified people. See zone valves and heating controls.

Sources