Confused by DIY terms? We’ve got you covered from A-Z with our Jargon Buster!
Regulates the temperature and flow of an opening from which air discharges.
Air release point
A place where air can be purposely released from a central heating radiator system.
A device fitted to a central heating system that eliminates any small bubbles of air circulating in the system water. This reduces circulation noise and can reduce corrosion.
A blockage in a water pipe caused by a trapped bubble of air, reducing or stopping the flow.
Automatic on-off switches (programmers and timers)
Devices that enable the central heating system to switch on and off at the times you choose.
Movement of the fluid from a downstream to upstream within an installation contrary to the intended direction of flow.
Balanced Flue appliance
Room sealed appliance which draws its combustion air from a point adjacent to the point at which the combustion products are discharged, the inlet and outlet being so disposed that wind effects are substantially balanced.
A valve for controlling the flow of water into a cistern, the valve being operated by the vertical movement of a float.
This can be caused by overheating due to a variety of reasons, a build-up of scale due to hard water, a faulty boiler thermostat, a lack of water in the system or the pump not working.
Used to release air that has gradually built up inside the radiator, preventing the panel from heating properly. If this does happen, check out our simple instructions on how to bleed your radiator.
An obstruction that could apply to a pipe or airway in a domestic appliance or central heating system.
Can prevent boiler waste products being safely taken outside of the building. Mechanical defects and debris can also cause blockages.
A boiler is an appliance in which water or other fluid is heated. The fluid is then circulated out of the boiler for use in heating applications. Faulty boilers should only be dealt with by a Gas Safe Registered engineer.
Passage for conveying combustion products to outside air.
Boiler flue thermostat
Heating system safety and control feature on a boiler that measures the temperature of gases entering the flue after the burner.
A device that collects temperature data from sensors inside and outside the building, allowing the boiler to work at maximum fuel efficiency.
A slotted screw or hexagonal nut with a plastic cap in the centre of a water circulating pump. Used to position the pump rota in place and can be used to vent the pump of air or free the rotor when stuck.
Central heating pressure
A constant flow of water pressure in your central heating system is an essential factor to a fully functional boiler.
Also known as a non-return valve, a device that normally allows a fluid to flow in only one direction.
Circuit board electronics
Electrical circuitry, often of low voltage and non-maintainable, found in most modern appliances.
The pressure at which a central heating system operates. Combination boilers and refrigeration systems have a critical circuit pressure at which they operate most efficiently and safely.
The main water flow and return pipes to and from the central heating boiler for the radiator circuit.
A device used to pump water within the central heating system. A non-ferrous type should be used for the hot water (where a standard cast steel pump would quickly rust away).
Fixed, vented container for holding water at atmospheric pressure.
Suitable for all central heating systems to protect against mineral oil contaminant.
The heating element in a domestic hot water tank. Known as the ‘primary circuit’, it circulates water from the boiler to indirectly heat hot water.
Cold mains supply
The potable (drinkable) water piped to the premises by the utilities or water company.
Cold water storage tank
A container for holding water, usually used for providing a feed to domestic cold water and/or to a vented domestic hot water system.
Boiler designed to provide domestic hot water and hot water for central heating without the need for additional secondary storage.
The area within the boiler where the main combustion of gas takes place.
Produced when fuel is burnt. They consist mainly of CO2 and water vapour.
Formed by using a tube nut being tightened on a thread to compress a compression ring (or olive) onto the outer face of the tube.
A pipe, usually plastic used to allow the safe removal of condense from an appliance.
Appliance designed to make use of the latent heat from water vapour in the combustion products by condensing the water vapour within the appliance
A component of an electrical power system containing fuses or breakers that splits the incoming electrical supply into current-protected circuits.
Appliance that is designed to heat a room mainly by the emission of air heated by convection
Heat your central heating system directly and produce hot water for your cylinder.
Conventional open flue
Chimney that evacuates the products of combustion to the outside air, the combustion air being drawn from the room or space containing the appliance.
An additional protective, non-rusting skin added to the primary metals of waterways to help them resist corrosion.
Central heating system corrosion results from hard-water deposits or from oxygenated water reacting with the system’s metal components. Boiler corrosion is the deterioration of boiler components due to reactions with its surroundings.
A corrosion inhibitor is a chemical compound that when added in small concentration stops or slows down corrosion in your boiler.
Process that is used to remove limescale (calcium carbonate) from heat exchanger waterways.
A device using differential pressures to operate or function . Common applications in a boiler are the diverter valve and air pressure switch.
A digital programmer has an electronic display, but does the same job as the time clock. It may have separate controls for the heating and hot water.
A radiator with two heating panels.
Drain the system
Term used when water from a central heating system is to be purposefully emptied.
A device to drain a system.
Ducted warm-air system (AGS)
A system using ducting to distribute the heating air.
Enclosure designed to accommodate water pipes and fittings, electrical cables and other services.
Different types of metals used in central heating systems, such as copper and aluminium, can act like a battery in the presence of mildly acidic water, present in some central heating systems, resulting in corrosion.
Most modern boilers have an electronic ignition which has replaced permanent pilot ignition systems (commonly referred to as pilot lights). When the appliance is required to generate heat (either for hot water or for heating the property), a spark is produced at the ignition electrode, supplied from an electronic spark generator, which in turn lights the gas burner of the appliance.
Emergency Control Valve ECV (Sometimes referred to as a gas shut off valve)
This is a device for shutting off the supply of gas in an emergency, which is intended to be used by the consumer of gas, and is installed at the end of a gas service pipe or gas distribution main. In domestic premises, this will be located in close proximity to the gas meter.
The English bond consists of alternating rows of stretchers (long faces) and headers (ends), with the alternative headers centred over and under the vertical joints of the stretchers. This is the strongest bonding arrangement possible as there are no continuous vertical joints within the thickness of the brickwork.
This is a tank, vessel or housing, designed and built to contain fluids under pressure such as water in a pressurised central heating system. Its purpose is to accommodate the increase in water pressure and volume when water is heated. Inside the vessel, heated water is separated from a volume of air by a rubber diaphragm. When the heated water expands, it exerts a force on this diaphragm, compressing the air on the other side.
Feed and expansion tank
A cistern or tank for supplying cold water to a hot water system without a separate expansion cistern, which also incorporates accommodation for the expansion of water when heated such as in heating and hot water systems.
A strip of impervious material, usually flexible metal (lead) that stops water from entering the junction between a roof covering and another material.
Flemish bond is a style of bricklaying which consists of alternating the long face and the ends of the bricks when laying them. The alternating brickwork gives a pleasing appearance but the internal bonding arrangement produces continuous, narrow, vertical joints parallel to the wall surface which may weaken the bond slightly.
A device fitted along with a water valve / ballcock to automatically maintain a desired water level in a water tank.
A duct that contains the flue of a chimney configuration.
Flue (Open flue)
A flue or chimney structure that removes the products of combustion to the outside air, with the air for combustion, being drawn directly from the room, space or enclosure containing the gas fired appliance.
Flue (room sealed)
A flue or chimney structure that removes the products of combustion to the outside air, with the air for combustion being drawn directly from the outside.
This is the wall of a chimney structure consisting of components the surface of which is in contact with the products of combustion, this includes a rigid or flexible liner inserted into a chimney to form the flue and the inner wall of a metal or masonry chimney construction.
Flue outlet (terminal)
A fitting on the outlet of the flue where the products of combustion discharges to the atmosphere.
A device which, by the melting of one or more of its specifically designed and proportional components, opens the circuit in which it is inserted by breaking the current when this exceeds a given value for a sufficient time. The fuse comprises all the parts that form the complete device.
Gas Safe Register
A list of engineers who are permitted to install and service gas boilers as approved by the Gas Safe Register.
Gas shut-off valve
This is usually located next to the gas meter. If the meter box is located outside then a gas key is usually required to open the box.
A visual device to obtain the value of a medium. For example, water pressure or temperature. Can be mechanical, electrical, or a combination.
The part of a connection that has to be physically tightened.
A seal used to prevent leakage between a fixed part and a moving part.
A water circuit that, being un-pumped, relies on the principle that hot water rises and cold water sinks. Where there is a heating source, circulation occurs.
A fitting of the underground surface water or waste water drain over which down-pipes, or other above ground (such as soil and vent pipes) drainage, discharge.
An isolation valve that has a circular grip for turning by hand.
Water that contains concentrates of soluble calcium carbonate greater than 20 parts per million.
Heat energy radiated from any source.
Heat exchanger coil
The device used to transfer heat energy to another medium, such as hot gases in a boiler transferred to the central heating water.
The rated output of an appliance, usually given in KW, BTU, or Therms.
The hot water pipe from a boiler to the radiator system.
The cooler water pipe returning the water from the radiator system to the boiler for re-heating.
A specific type of valve used to control the flow of water or steam in a hydronic heating system allowing heat to be directed at specific zones.
This is caused by overheating due to a variety of reasons, including a blocked chimney, a build-up of scale due to hard water, a faulty boiler thermostat, a lack of water in the system or the pump not working.
A service channel that lies parallel with the ground.
Hot water circuit
The water circuit from the boiler to the hot water storage tank.
Hot water cylinder
Hot water passes through the cylinder, heating up the stored water.
Hot water cylinder thermostat
The thermostat controls the temperature of hot water stored in the cylinder. It is usually fitted to the tank with a temperature sensor.
Hot water storage tank
Stores the domestic hot water.
Hot water thermostat
This will be fitted to the side of the hot water tank. It controls the highest temperature of the hot water. Some boiler systems don’t need them.
A component, or device, with a passage that has the ability to control substances entering an appliance.
A decorative trim, usually of metal wood or plastic, that runs along the bottom of the front of a cupboard or cabinet unit, freezer, fridge, dishwasher or washing machine. The kick plate protects it from damage and wear, and hides any feet or components behind it.
Used to broadly identify the larger copper pipe sizes over 28 millimetres commonly used for plumbing and central heating systems.
Abbreviated from Liquid Crystal Display, it is an electronic visual display that can be found fitted as a flat panel on boilers and programmers and gives information regarding that appliance.
Is a hard off-white, calcium deposit that can be found in the primary water side of an inadequately protected central heating system especially in hard water areas.
It can damage a boiler’s heat exchanger and other water carrying components, cause water leaks, and reduce the reliability, efficiency, and effectiveness of the central heating system.
A manually operated control valve that requires a purpose-made tool to use.
Water supplied directly to the home through a network of underground pipes by the utilities or water companies.
Metal heat exchanger
Heat exchanger made from a metal.
Microbore pipes are used to feed the radiators from centrally placed manifolds. A system can use 8, 10, 12, or millimetre copper or polypropylene pipe. The main advantages of the system is that the smaller pipes contain less water so heat from the boiler is transferred quicker and more efficiently to the radiators. Also, it is simpler and less expensive to install.
Automatically adjusts gas throughput dependant on temperature and demand.
A fitting designed to allow a fluid or a gas to flow in one direction only. Can be also known as a “One Way Valve”, “Check Valve” or “Clack Valve”.
The component in a compression fitting that provides the mechanical seal.
Where the radiators are run in series, with the flow in and return out on the same pipe.
Open safety-vent pipe
The part of a conventional tank-fed un-pressurised central heating system that allows any pressure build up to be safely discharged to the atmosphere.
A conventional central heating system which is un-pressurised and tank fed.
A device that collects temperature data from sensors inside and outside the building, allowing the boiler to work at maximum fuel efficiency.
An isolation device to control substances leaving an appliance.
A device fitted to a tank to safely discharge surplus water.
A method of heating involving the installation of the heating units (pipe coils) in the walls, floor or ceiling of the room.
A heating unit placed on, or flush with, a flat wall surface and intended to function as a radiator.
A panel that is usually fitted across the front of a cabinet to dissipate the heat and add to the unit’s appearance.
A small gas flame, usually natural gas or liquefied petroleum gas, which is kept alight in order to serve as an ignition source for a more powerful gas burner.
The connection point between two pipes, or a pipe and a component.
A roof with two or more slopes at more than 10 degrees to the meeting point.
Surfaces that have tiny openings which allow liquid to be absorbed, or to pass through.
A gadget to tell the pressure of the water in the system pipe work.
A storage container, designed to hold liquids at a pressure substantially different from the ambient pressure.
Primary heat exchanger
Main heat exchanger in a boiler, usually serves the radiator system.
A mechanical, electrical, or combination device incorporating a timer that can be pre-set to enable a central heating system to be turned on or off at intervals to suit the consumer.
Also called plumber’s tape. A thin film cut to specified widths for use in sealing pipe threads.
A device used to circulate water around the central heating system and/or hot water cylinder.
The part of a circulating pump that drives the water.
The water port on the circulating pump that the water flows out from.
Transfers the heat from the water in the central heating system to the rooms.
A decorative or protective surround for a radiator.
Used to control and isolate the water flow and return on a radiator.
An electrical component, often found on the ‘PCB’ used to switch secondary equipment such as water pumps, gas valves, and flue fans.
Controls the temperature by means of simple on-off switching of the boiler (or the pump, if the boiler has to run constantly in order to provide hot water).
A common term for corrosion of iron and its alloys, such as steel, formed by the reaction of the metal with oxygen in the presence of water.
A device used to prevent the build up of excessive pressure.
Scale is a build-up of calcium deposits due to hard water.
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.
A drainpipe that carries off wastes from a plumbing fixture, especially from a toilet.
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.
A device, as in a home heating system, that automatically responds to temperature changes and activates switches controlling the equipment.
Temperature pressure relief valve (TPV)
A component that discharges water from a cylinder at a temperature of 90-95 degrees Celsius.
Thermostatic radiator valve (TRV)
Sense the air temperature around them and regulate the flow of water through the radiator which they are fitted to. They do not control the boiler.
A time clock has a dial. Around the edge of the dial, matching the hours of the day, are ‘pins’ that you can push in or out. These pins tell the system to turn on or off during the times you have selected.
Timers and programmers
Timers switch the system on and off at set times of the day. Programmers offer a larger number of on-off programmes, giving the consumer greater flexibility and control.
If your radiators or heating system seem to be making a noise then it may mean that there is air trapped somewhere. Air commonly gathers in the upstairs radiators. This air can be easily removed by bleeding the radiators.
Two-pipe (vented) system
A heating system that transmits heat quickly and directly to all radiators in the circuit, raising them all to the same temperature. The flow of water through each radiator on this type of system must be regulated to achieve an average temperature to each heat emitter.
A mechanical device for halting or controlling the flow of a liquid, gas, or other material through a passage, pipe, inlet, outlet, etc.
Movement of air and its replacement with fresh air due to wind, temperature gradients or artificial means, for example fans or extractors.
Opening, generally with a security grille, used for ventilation.
Warm air systems are similar to air conditioning units in the way that they blow air around a network of ducts and out through grilles or vents throughout the house. The air is normally heated by way of a gas burner and is controlled by a room thermostat and a time switch.
A small flat metal, rubber, or plastic ring fixed between two joining surfaces or between a nut and a bolt to spread the pressure or act as a spacer or seal.
Wet central heating
A wet central heating system pumps hot water into your radiators, which in turn heat your home.
A control device for the flow of water or steam to areas, or zones, of a building.