Jargon buster

Here are some plumbing terms and there meanings

Air admittance valve

A valve designed to vent a stack pipe within a building by drawing air into the pipework when an appliance is discharged. The valve automatically reseals the pipework when the air pressure equalises so that foul air is contained within the pipework - also referred to as a Durgo valve.


A bubble of air that gets to the top section of piping or radiators and cannot be pushed out by the contents and either reduces the flow of water or creates a cold spot in radiators.


The unit of measurement of water pressure - one bar is approximately equivalent to a column of water 10m high or 14.5 lbf/inĀ² or 100 kPa (kilopascal).

Combi boiler

Combination or combi boilers combine the central heating with domestic hot water in one device. These boilers require less space than conventional tanked systems, and are cheaper to install, since water tanks and associated pipes and controls are not required.

Immersion heater

An electrical water heater inserted into a hot water cylinder - it incorporates both the heating element and the thermostat). Two may be used with a single cylinder - one on 'off peak' electricity, the other switchable for use at other times if necessary.

Mixer shower

A simple shower using a valve to combine the domestic hot and cold water supplies to provide the required temperature and flow.

Pressure relief valve

A safety device fitted to relieve excessive pressure within a heating boiler or system. Will reset itself once the excess pressure has been relieved.

U bend

A U-shaped system os pipework, which maintains a residual amount of the waste water at the base of the U to prevent the smell from the drains coming back into the house.