UK Plumbing Glossary
The words UK plumbers use, defined in plain English, each linked to the topics where the plumbing path teaches it.
Before you start: some plumbing work is regulated or notifiable
Some water fittings work needs notice to, and consent from, the water supplier before it starts. Check the rules where you live.
Gas work is for competent workers covered by a Gas Safe registered business in Great Britain. Northern Ireland has separate gas regulations. Do not work on gas pipes or appliances yourself.
In England, installing an unvented hot-water system over 15 litres is notifiable building work: use a competent installer registered with a competent-person scheme, or tell building control before work starts. Leave this work to a suitably skilled person.
Wales, Scotland and Northern Ireland have their own water and building rules; check which apply before work starts. Electrical connections belong with an electrician.
This guide does not qualify you or make you competent, approved or registered for plumbing, gas or unvented work.
Search a term or another name for it. Open a definition to compare meanings, then follow the entry to explore related ideas.
9 of 9 terms
A
- Air gapA physical gap between the outlet of a pipe or tap and the highest level the water below it could reach, so that water cannot be drawn back into the supply.
Show Air gap definition
A physical gap between the outlet of a pipe or tap and the highest level the water below it could reach, so that water cannot be drawn back into the supply. Because there is nothing in it that can fail, an air gap is the protection used against the highest-risk water, such as a category 5 source. A tap whose spout sits well above the spill-over level of a basin is a familiar example.
Path section: Cold Water Basics
B
- BackflowWater flowing the opposite way to the one intended, for example from a hose left in a bucket, a cistern or an appliance back into the pipe that supplies drinking water.
Show Backflow definition
Water flowing the opposite way to the one intended, for example from a hose left in a bucket, a cistern or an appliance back into the pipe that supplies drinking water. It can happen when the supply pressure drops, or when the system downstream is at a higher pressure. The water fittings rules in each UK nation require protection against it that matches the risk, judged by fluid category.
Path section: Cold Water Basics
C
- Compression fittingA joint on water pipework made by tightening a nut over a ring called an olive, which squeezes onto the pipe and seals it.
Show Compression fitting definition
A joint on water pipework made by tightening a nut over a ring called an olive, which squeezes onto the pipe and seals it. It needs no heat, which makes it useful where soldering would bring a fire risk, and it can be taken apart later. Too little tightening leaves it weeping, and too much can distort the olive.
Path section: Pipework & Jointing
F
- Fluid categoryA scale of five categories that grades water by the harm it could do if it flowed back into drinking water.
Show Fluid category definition
A scale of five categories that grades water by the harm it could do if it flowed back into drinking water. Category 1 is wholesome drinking water and category 5 is the most serious risk, such as water that may contain human waste. The higher the category, the stronger the backflow protection needed between that water and the supply.
Path section: Cold Water Basics
I
- IsolationIn plumbing, turning off the water to the part of a system you are working on, then proving it is off by opening an outlet and checking that the flow stops.
Show Isolation definition
In plumbing, turning off the water to the part of a system you are working on, then proving it is off by opening an outlet and checking that the flow stops. Isolate as close to the job as possible, with a service valve where there is one and the stop tap where there is not, and drain the section down before opening it up.
Path section: Isolation, Hot Water Safety and Simple Repairs
S
- Service valveAlso called Isolating valve
Show Service valve definition
A small valve on the pipe to a single tap, cistern or appliance, so that one outlet can be turned off without shutting off the whole house. Many are quarter-turn: the slot or lever lines up with the pipe when the valve is open and sits across it when closed. Turning one off and then opening the outlet shows whether it has worked.
Path section: Isolation, Hot Water Safety and Simple Repairs
- Stop tapAlso called Stopcock
Show Stop tap definition
A valve that shuts off the cold water supply to a building or to part of it. Most homes have an internal stop tap where the supply pipe comes in, often under the kitchen sink, and another outside near the boundary, usually under a small cover. Knowing where the internal one is, and checking that it turns, is the first step in dealing with a leak.
Path section: Cold Water Basics
T
- Temporary continuity bondA lead with a clamp at each end, fitted across a metal pipe before a section of it is cut out or removed, so that any electrical path through the pipework is not broken while the work is done.
Show Temporary continuity bond definition
A lead with a clamp at each end, fitted across a metal pipe before a section of it is cut out or removed, so that any electrical path through the pipework is not broken while the work is done. Metal pipes can be part of a building's bonding, and opening one without a bond in place can leave someone bridging the gap. Any change to the permanent bonding belongs with an electrician.
Path section: Safe Working
U
- Unvented cylinderA hot-water cylinder fed straight from the mains with no open vent or cold storage cistern, so it stores hot water under pressure.
Show Unvented cylinder definition
A hot-water cylinder fed straight from the mains with no open vent or cold storage cistern, so it stores hot water under pressure. It depends on safety devices, including temperature and pressure relief, and on discharge pipework that carries hot water away safely if they operate. Recognise one and hand it over: in England, installing an unvented hot-water system that holds more than 15 litres is notifiable building work, done by a competent installer registered with a competent-person scheme or with building control told before work starts. Wales, Scotland and Northern Ireland have their own building rules.
Path section: Isolation, Hot Water Safety and Simple Repairs
Terms every trade shares
These apply to plumbing just as they do to other trades, so each has one page in the main glossary.
Connect the name of a part to its purpose
Updated
Use a system sketch as you read
Place the supply, stop tap, service valve and outlet on a simple sketch. Add a storage vessel where relevant and consider how water could return towards a drinking supply. Definitions become easier to use when the parts have a location and a purpose.
Questions to take further
- Does isolation mean the same thing in plumbing and electrical work?
- Both concern making a system safe for the intended work, but the hazards, equipment and verification differ. Turning off water does not establish electrical safety, and neither operation automatically removes stored pressure or heat.
Sources
- Skills England: plumbing and domestic heating technician — The range of plumbing systems and skills in the England occupational standard.
- Water Regs UK: backflow protection — Contamination risks and the selection of appropriate backflow protection.