Jargon Buster - S

Confused by DIY terms? We’ve got you covered from A-Z with our Jargon Buster!

Safety Valve

A device used to prevent the build up of excessive pressure.


Scale is a build-up of calcium deposits due to hard water.

Sealed system

This is an alternative to the open vented method. As the name implies, the system is closed, no water tanks are needed and the hot water is supplied direct from the mains.

Secondary heat exchanger

Term used to describe the smaller DHW (domestic hot water) unit in a boiler.


Stem or shaft of a valve that connects the wheel to the valve seat.

Skirting heaters or radiator

Designed for installation in place of wooden skirting board. These tend to have relatively low output per unit length but do even out the heat input around the room.


Black sludge (magnetite) clogs the pump and builds up in the bottom of radiators, reducing their heat output.

Small-bore copper or plastic pipes

General term to identify 15 millimetres and 22 millimetre pipes.

Small-bore two-pipe system

Microbore pipes are used to feed the radiators from centrally placed manifolds. This system uses 10 millimetres or 12 millimetres copper or plastic pipe. The main advantage of the system is the smaller pipes contain less water so less heat is lost along each pipe run.

Soil pipe

A drainpipe that carries off wastes from a plumbing fixture, especially from a toilet.

Solid-fuel boiler

Any fuel that is not a liquid or gas, such as coal, wood, anthracite, etc.


Similar to a shank.


A soil vent pipe

Standard universal backplate

A mounting plate fixing for a component.


The stopcock controls the flow of water and shuts off the entire supply in an emergency. The stopcock can usually be found under the kitchen sink, bathroom, cloakroom, cellar or basement.

Storage vessel and heating vessel

A hot water storage vessel is usually in the form of a cylinder, usually located in an airing cupboard, a heating vessel can be located within a boiler or separately and is the same as a pressure vessel.

Swarf and flux

Over time, sludge, debris, copper swarf, flux, etc will collect in your central heating system. If you find that your radiators have cold spots or simply have poor circulation then this may be down to excessive sludge within the system.


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