Plumbers A–Z dictionary

B

Backflow

Unwanted reversal of water movement which can contaminate a supply. Protection depends on the actual risk and installation.

Boiler replacement

Boiler replacement exchanges a heat source as part of a compatible heating and hot-water system. The work may also require controls, flue, pipework, condensate, treatment and commissioning changes. A new appliance alone does not prove retained radiators, cylinder or distribution are suitable or that every existing comfort problem will disappear.

Boiler service

A boiler service is planned maintenance and examination carried out to the boiler manufacturer’s instructions. For a gas boiler, use a Gas Safe registered engineer competent for the appliance. A service is not simply a visual look at the casing and is not automatically the same booking as a landlord’s gas safety check.

Bottle trap

A bottle trap is a waste fitting with a chamber arranged to retain a water seal beneath an appliance such as a basin. The seal helps separate room air from the drainage system. The fitting is not simply a decorative cover, and its suitability depends on the fixture and pipework arrangement.

C

CO alarm

A carbon monoxide alarm detects carbon monoxide and alerts occupants according to its design. Carbon monoxide is a poisonous gas associated with incomplete combustion and cannot reliably be recognised by smell. An alarm is a protective warning device, not a substitute for safe appliances, appropriate ventilation and competent maintenance.

Combi boiler

A combi, or combination boiler, provides central heating and heats domestic hot water on demand within one appliance. A conventional combi normally avoids a separate hot water cylinder. Combi describes its functions; condensing describes heat recovery from combustion gases. A boiler can therefore be both a combi and a condensing appliance.

Condensate pipe

A boiler condensate pipe carries liquid produced during condensing operation to an appropriate discharge arrangement. It is different from the flue, pressure-relief discharge and domestic hot-water supply. Correct routing, material and termination depend on the appliance and installation, not merely the appearance of a plastic pipe outside a wall.

Copper pipe

Copper pipe is metal tube used in suitable building-service systems, including water and heating. The word copper identifies a material, not a complete specification. Dimensions, condition, application and jointing compatibility matter, especially when connecting new work to an older installation or a different material.

D

Dead leg

A branch serving an outlet which is unused or rarely used. Low turnover can matter for water hygiene.

Dynamic pressure

Pressure measured under stated flowing conditions. It must not be confused with a static reading taken when no relevant outlet operates.

E

Expansion vessel

An expansion vessel provides a compressible gas space to accommodate changes in water volume as a system heats. A flexible diaphragm or similar separation commonly keeps the gas and water apart. Vessels used for sealed heating and those suitable for drinking-water services are not interchangeable merely because their size or colour looks similar.

F

Flow rate

Volume delivered over time under specified conditions. Strong static pressure alone does not guarantee adequate simultaneous outlet flow.

G

Gas safety check

A gas safety check assesses whether the relevant gas appliances and flues are safe to use at the time of the visit. It is not the same appointment as a full boiler service, even though some checks overlap. In Great Britain, use a Gas Safe registered engineer qualified for the particular work.

Getting into chimney sweeping

Chimney sweeping is the controlled cleaning and assessment of relevant flue arrangements within an agreed scope. It is distinct from unrestricted appliance servicing, structural certification or gas work. A career route should develop practical judgement, protection of the home and clear reporting of what a sweep can and cannot establish.

Getting into heating engineering

Heating engineering covers the design, installation, maintenance and diagnosis of heating systems within a person's competence. It overlaps with plumbing and gas work but is not identical to either. A useful route teaches heat demand, water distribution and controls while making fuel, refrigerant and electrical boundaries clear.

Getting into plumbing

Plumbing covers water supply, sanitation and related building services. A trainee learns installation, testing and fault diagnosis while protecting people and property from leaks and contamination. A plumbing qualification does not automatically authorise gas work, refrigerant handling or every heating-design responsibility.

Getting into pool engineering

Pool engineering brings together circulation, filtration, water treatment, heating and construction-related systems. Domestic pool maintenance and commercial plant operation are not identical roles. A good entry route develops supervised practical competence and clear specialist boundaries rather than treating a chemical test kit as qualification for every pool system.

H

Heat loss calculation

A heat loss calculation estimates how much heat a building or room needs to maintain a chosen indoor temperature under defined outdoor conditions. It informs heating design rather than simply matching a new appliance to the old one.

Heat only boiler

A heat-only boiler, often called a regular or conventional boiler, supplies heat to a suitable external heating and hot-water arrangement. The name distinguishes it from a combi, which produces domestic hot water on demand. It does not, by itself, specify every pump, tank, cylinder or pressure arrangement in the home.

Heating inhibitor

Heating inhibitor is a specified treatment used in suitable closed heating-water systems to help limit corrosion and related deterioration. It is not drinking-water treatment, antifreeze by default or a chemical that repairs leaks. Product compatibility, concentration and the system's condition determine its appropriate use.

Hot water cylinder

A hot water cylinder stores heated water for domestic use. It may be vented or unvented and may be heated directly by an immersion heater, indirectly through a heat exchanger, or by a combination of sources. The cylinder's usable service depends on its system design, not simply the volume printed on its label.

I

Isolation valve

A valve intended to shut off a defined section or appliance. Its location should remain accessible and its purpose clear.

L

Leak detection

Leak detection is the investigation used to locate unwanted water escape and distinguish its source. It can concern a buried supply, internal plumbing, heating pipework or waste drainage. Finding where a surface is wet is not always the same as finding where the water escaped: moisture can travel through a building before becoming visible.

M

Magnetic filter

A magnetic heating-system filter is a component designed to capture suitable ferrous debris circulating in the system water. Some products combine magnetic and other separation functions. It is not a drinking-water filter and does not remove every contaminant or repair the cause of ongoing corrosion.

P

Potable water

Water suitable for drinking. Materials, backflow protection and maintenance must preserve the relevant water quality.

Power flushing

Power flushing is a particular approach to cleaning suitable wet heating systems with specialist circulation equipment and an appropriate treatment process. It is not a universal cure for cold radiators or boiler faults. Diagnosis should establish whether contamination is present, whether cleaning is needed and which method the system can safely tolerate.

Press fitting

A press fitting makes a mechanical pipe connection using a specified pressing tool and matching components. It is different from a push-fit connector or a soldered capillary joint. The fitting, pipe, seal, jaw profile and application must form an approved compatible arrangement; physical fit alone is not evidence of suitability.

Pressure reducing valve

A device controlling downstream pressure within its design conditions. It is not interchangeable with a safety relief valve.

PTFE tape

PTFE tape is a thread-sealing material used where the joint design and product instructions permit it. It is not universal plumbing glue. Some connections seal on threads, while others use a washer, O-ring, olive or another specified surface; putting tape on every visible thread can misunderstand how the joint works.

Push-fit fitting

A push-fit fitting joins suitable pipe using an internal retaining and sealing arrangement rather than a soldered joint. Domestic water products may use a grab ring, an O-ring and a release mechanism, but designs differ. The term describes a jointing method, not permission to combine any pipe and fitting of a similar nominal size.

Q

Quarter turn valve

A valve operated through approximately a quarter turn between open and closed positions. Select for the fluid, pressure, temperature and required function rather than the handle shape alone.

R

Radiator balancing

Radiator balancing adjusts water distribution through a heating system so that radiators receive an appropriate share of flow. It is different from bleeding air out of a radiator.

Run

A continuous route or length of pipework; other trades use it for cables, cabinets and similar sequences. State the endpoints.

S

Stopcock

A stopcock is a valve used to shut off a water supply, commonly the incoming mains supply to a home. People also say stop tap. Its location and the area it isolates matter more in an emergency than its appearance. A small service valve beneath a basin may isolate only one fitting, not the entire property.

System boiler

A system boiler heats a central heating circuit and normally works with a separate hot water cylinder. It generally incorporates key heating system components within the boiler casing.

T

Tail

A short connecting section, such as a tap tail or radiator tail. State which fitting and size are needed.

Thermostatic mixing valve

A thermostatic mixing valve, or TMV, blends hot and cold water to deliver a controlled mixed temperature at an outlet. It is used to manage scalding risk where appropriate. It does not replace the controls which keep a cylinder safe, and it is not a reason to turn stored hot water down indiscriminately.

Thermostatic radiator valve (TRV)

A TRV controls flow through a radiator in response to the temperature around its sensing head. It helps regulate a room; it does not directly select the boiler's water temperature.

Trap seal

Water retained in a waste trap to limit passage of drain air. Evaporation, siphonage or faults can compromise it.

Tundish

A tundish is an open-ended fitting which provides a visible break in a discharge route. In domestic plumbing it is often seen in the safety discharge pipework of an unvented hot-water cylinder. Its purpose is not simply to join two pipes: the visibility and separation are part of the intended safety arrangement.

W

Water hammer diagnosis

Water hammer diagnosis investigates pressure surges and associated noise caused by rapid changes in water flow. A bang when a valve closes may be water hammer, but noisy pipework can also involve loose supports, vibration, thermal movement or a faulty component. The sound alone does not establish which repair is needed.

Water pressure testing

Water pressure testing can mean measuring the supply's operating pressure or testing pipework for integrity under specified conditions. These are different tasks. A useful booking makes clear whether the problem is poor shower performance, excessive pressure or proving that newly installed plumbing is watertight before it is concealed.

Water softener installation

Water softener installation adds equipment which reduces water hardness, commonly by ion exchange, together with the necessary pipework, controls and drainage arrangements. A softener is not the same as every product described as a conditioner, and neither description means the equipment makes unsafe water fit to drink.

Weather compensation

Weather compensation adjusts a heating-system target in response to outdoor conditions. In a compatible system, it can vary the required flow temperature as the weather changes instead of relying only on a fixed high setting. It is different from load compensation, which responds to the relationship between indoor conditions and demand.

Y

Y strainer

A fitting with a mesh screen that collects debris from a fluid system. It needs correct orientation, isolation and access for cleaning under the manufacturer’s instructions.

Sources and further reading

Linked article sources support the technical background; informal usage is editorial and varies by region. Full specification and legal requirements must be checked in the original.

• Baxi: operation and suitability
• Gas Safe Register: boiler guide
• www.hse.gov.uk/gas/domestic/faqownerocc.htm
• GOV.UK: Approved Document L
• GOV.UK: Approved Document G, hot-water safety
• Gas Safe Register: check and service differences
• HSE: appliances and landlord gas checks
• Energy Saving Trust: weather and load compensation