"A" Rated

This is synonymous with "Condensing" or "High Efficiency", although both these terms can refer to A and also B rated boilers. All boilers that are A rated are High Efficiency, or HE.

 Adjustable Damper

Regulates the temperature in the room by controlling heat emissions.

 Air Release Point

A place where air can be purposely released from a central heating radiator system.

 Air Separator

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 Corrosion

 Airlock

A blockage in a water pipe caused by a trapped bubble of air, reducing or stopping the flow.

 Aluminium Extrusion

A machine pressed metal component made of aluminium.

 Automatic On-Off Switches  

Devices that enable the central heating system to switch on and off at the times you choose.

 Back Boiler Units

Back Boiler Units are fitted into fireplaces that may already have an existing fire front. This type of boiler is a space saver, but higher outputs can be an issue because of the size limitations. Other considerations are a path to the outside for ventilation. BBU are used in traditional systems, and cannot have a sealed radiator system because their power output is not great enough.

 Backflow

A flow in a direction contrary to the intended normal direction of flow, usually caused by siphoning. Can also be the result of an incorrectly functioning diverter valve.

 Balanced Flue

A flue system designed by the boiler manufacture, which permits flexibility in terminal location i.e. low level, vertically or horizontally.

 Ballcock

Also called a balltap or fill valve. A mechanism for filling water tanks, such as those found in flush toilets, and avoiding overflow.

 Bio-fuel

An energy source derived from renewable material (such as wood, wheat or oilseeds) that be burned to generate heat, power or motion.

 Bio-liquid

A liquid bio-fuel.

 Bleed Valve

Used to release air that has gradually built up inside the radiator, which prevents the panel from heating properly.

 Block

An obstruction that could apply to a pipe or airway in a domestic appliance or central heating system

 Boiler Fume Thermostat

Heating system safety and control feature on a boiler that measures temperature of gasses entering the flue after the burner.

 Boiler-Energy Manager

A device that collects temperature data from sensors inside and outside the building allowing the Boiler to work at maximum fuel efficiency.

 BTU

The British Thermal Unit. A way of measuring heat energy, defined as the energy needed to raise the temperature of one pound of water by one degree Fahrenheit. 10,000 BTUs is equivalent to 2.92997kW.

 Bund

An enclosure inside which an oil storage tank can be located which is capable of holding the contents of the oil storage tank plus 10% so as to prevent oil damaging the environment in the event of a leakage or spillage. Bunds use to be known as catchpits.

 Cap-Nut

A slotted screw 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.

 Check Valve

Also known as a non-return valve, it allows liquid to flow in one direction only. Commonly fitted to Combination Boilers, they allow water to flow to Radiators and prevents the water returning back into the water main.

 Circuit Board Electronics

Electrical circuitry, often of low voltage and non-maintainable, found in most modern appliances.

 Circuit Pressure

The pressure in which a central heating system operates at. Combi boilers and refrigeration systems have a critical circuit pressure in which they operate most efficiently.

 Circulation Pipe

Are the main water flow and return pipes to and from the central heating boiler for the radiator circuit. The normally smaller diameter pipes to the radiators are known as "branches".

 Circulation Pump

A device used to pump water to 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.

 CIRIA

Construction Industry Research and Information Association

 Cistern

Is a container holding a small amount of water usually used for flushing toilets.

 Cleanser

This is suitable only for traditional or open-fuel boilers, not Combination Boilers.

 Coil

Is the heating element in a domestic hot water tank. Known as the 'primary circuit' it circulates water from the Boiler to give hot tap water.

 Cold Mains Supply

Is the potable (drinking) 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.

 Combination (Combi)

Combination (Combi) boilers heat the hot water on demand by a heat exchanger in the boiler. There is no need for a hot water storage tank. Installation is often quicker and cheaper than a traditional type system.

 Combustion Chamber

Is the area within the Boiler where the fuel is burnt.

 Combustion Gases

Are the products produced when fuel is burnt. They consist mainly of Co2 and water vapour.

 Compression Fitting

Forms a joint with a mechanical seal and not soldered, glued or otherwise bonded.

 Condensing Boiler

A high efficiency boiler that recovers the heat from the flue gases which would otherwise be lost to atmosphere.

 Consumer Unit

Is a device that splits the incoming electrical supply into switched over current protected circuits.

 Copper-Lined Waterway

Is where the primary metals have an additional protective non-rusting skin added to resist corrosion.

 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.

 Cylinder Thermostat

A switching device fitted to the domestic hot water cylinder which controls the temperature of stored water. This should not be higher than 60 degrees centigrade.

 De-aeration Device

A device fitted in the oil line close to the heating appliance to help the draw of oil up to a level higher than the level of oil in the tank. It does this by removing the air and vapour create when the pump in the oil boiler applies suction to the high level oil line.

 Defrosting Resistance

This is a heater used to defrost the evaporator in a frost-free freezer or fridge.

 De-scaling

Process that is used to remove Limescale (calcium carbonate) from Boiler waterways.

 Diaphragm

Is a device used to compare different pressures. Common applications in a boiler are the diverter valve and air pressure switch.

 Digital Programmer

A digital programmer has an electronic display, but does the same job as the Time Clock. It has separate controls for the heating and hot water.

 Domestic Hot Water Cylinder

A storage vessel normally made of copper in which domestic hot water is stored. Inside the cylinder is a coil of pipe through which water from the boiler passes to heat the water, which becomes available through the hot water taps.

 Double Radiators

A Radiator with two heating panels.

 Double-Skinned Metal Panel

Manufactured from two metal sheets for extra strength.

 Drain the System

Term used to purposely empty the water from a Central Heating System.

 Draincock

A valved device to drain a system.

 Ducked Duct Warm-Air (Gas)

A system where the gas is combusted to give hot air which is distributed through the property.

 Ducting

A purpose made passageway to allow the installation of water pipes, electrical cables, etc.

 Electrolytic Action

Different metal types, such as copper and aluminium, act like a battery in the acidic water that is present in some central heating systems resulting in Corrosion

 Electronic Gauge

An electronic gauge includes a transmitter, probe and receiver. The transmitter sends a signal indicating the level of oil in the oil storage tank to a remotely located receiver and display unit. The probe is a sensor located within the oil storage tank that detects the level of oil in the oils storage tank, this is connected to a transmitter. The receiver picks up the signal from that transmitter and displays the level of oil in the oils storage tank.

 Electronic Ignition

Most modern Boilers have an electronic ignition that lights the burner automatically when the heating system controls call for heat.

 Expansion Tank

Small tank used in a central heating system to absorb water pressure and extra volume of hot water as it is heated. The tank contains a rubber Diaphragm which squeezes a small volume of air in the tank as the water expands, relieving pressure.

 Expansion Vessel

Expansion vessel is often inaccessible without the help of a Corgi registered engineer. Failure of the expansion vessel can result in a pressure rise as the system heats up too much and the relief valve opens.

 Fan Assisted Convector Heater

Is an appliance where an electric fan is used to distribute the warmed air.

 Feed-and-Expansion Tank

Provide water for the heating system and the domestic hot water cylinder while acting as a reservoir for any overflow as a result of expansion.

 Finned Pipe

Designed to give greater heat output.

 Finned Radiators

Fins give greater area to dissipate heat thus increasing the heat output of the Radiator.

 Fins

Designed for greater heat sink.

 Float (faulty or leaking)

A device fitted along with a water valve / Ballcock to automatically maintain a desired water level in a water tank.

 Floor Standing Boiler

Floor standing boilers can be traditional or combi and are seated on the floor. Floor Standing boilers can fit in spaces between kitchen units or, in larger homes, in a pantry or a garage.

 Flue

A flue is a pipe or chimney that is used to vent the waste gases, from the combustion process in the boiler, to the outside of the property. The waste gases are mostly carbon dioxide and steam. There are several types of flue, some boilers accommodating all types and some just one.

 Flue Liner

An insulated liner within an existing chimney that ensures expelled gases are at the right temperature and ensures there is a sufficient draw of outside air to maintain correct combustion.

 Flue Outlet

Is the point where the Boiler flue discharges to the atmosphere.

 Furnace

Used to describe household heating systems based on a central furnace known either as a Boiler or a Heater.

 Fuse

A device to protect an electrical appliance, or circuit, against excessive current flow (in amperes) above the appliance, or circuits, rated value.

 Gas Safe Register

The trade body which registers and certifies qualified heating engineers

 Gas Shut Off Valve

This is usually located next to the gas meter. If the meter box is located outside, then you would usual need a gas key to open the box.

 Gauge

A visual device to obtain the value of a medium. For example, Water Pressure or Temperature. Can be Mechanical, Electrical, or a combination.

 Gland Nut

Is the part of a connection that has to be physically tightened.

 Gland Packing

A seal used to prevent leakage between a fixed part and a moving part.

 Gravity Circulation

Is a water circuit that, being un-pumped, relies on the principle that hot water rises and cold water sinks, therefore, where there is a heating source, circulation occurs.

 Gully

A fitting of the underground surface water or waste water drain over which down-pipes, or other above ground (i.e. Soil & Vent Pipes) drainage, discharge.

 Handwheel Valve

An isolation valve that has a circular grip for turning by hand.

 Hard Water

Is water that contains concentrates of soluble calcium carbonate greater than 20 PPM.

 HE

High Efficiency. This is the title given to boilers which have a SEDBUK Rating of A or B.

 Heat Emission

Heat energy radiated from any source.

 Heat Exchanger Coil

Is the device used to transfer heat energy to another medium, i.e., hot gasses in a Boiler transferred to the central heating water.

 Heat Output

Is the rated output of an appliance, usually given in KW, BTU, or Therms.

Heating Cover

Heating Cover is an insurance policy which covers against Boiler and Heating Emergency

Heating Flow

Is the hot water pipe from a boiler to the Radiator system.

 Heating Return

Is the cooler water pipe returning the water from the Radiator system to the boiler for re-heating.

 Horizontal Duct

Service channel that lies parallel with the ground.

 Hot Water Circuit

Is 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 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.

 Inhibitor

Chemicals introduced into your central heating system that will slow down the rusting process of your radiators. We recommend that good quality brands (Kamco, Fernox, Sentinal), are used and handled by a professional, and introduced following a power flush and topped up every three years.

 Inlet Valve

Isolation device to control substances entering an appliance.

 Integrally Bunded Tank

An oil storage tank that is constructed at the factory to include a bund facility plus a lid to keep the bund clear of rain water.

 Kerosene

This is a light, low sulphur and very clean burning heating oil suitable for use with most types of oil and cooking appliance. Also known as 28 second, Class C2 to BS 2869

 kW

Equal to 1000 Watts. 1 Watt is defined as one Joule of energy released per second. 1kW is equivalent to 3413 BTUs.

 LPG

Liquid Petroleum Gas. An alternative to mains gas that requires a storage tank. LPG conversion kits can be obtained for many boilers, though currently it is a more expensive alternative to natural gas.

 LPG Powered Boiler

Liquid petroleum gas has many of the same advantages of mains gas but is considerably more expensive to use. LPG can also be used with other household equipment such as cookers and fires. As with oil, LPG requires a storage tank, or can be provided in replaceable cylinders. The range of LPG boilers available is considerably less than mains gas. Gas boilers can be converted to LPG with the appropriate conversion kit. It is a legal requirement that an LPG boiler is fitted by a CORGI registered engineer.

 Mains Water

Water supplied by the Utilities or Water Companies.

 Metal Heat Exchanger

Heat Exchanger made from metal.

 Microbore

A system of small pipes 8mm or 10mm in diameter. It is quick and easy system to install, but has limitations with regards to additions, alterations and maintenance. It is unsuitable to power flush but efficiency can be improved through introduction of a magnetic filter.

 Modulating Burners

Automatically adjusts gas throughput dependant on temperature and demand.

 Motorised valves

An electrically powered valve for the control of water flow through pipes, it can be operated by a time switch or thermostat.

 Natural Gas Boiler

Natural Gas is a clean fuel, burning with by-products of steam and carbon dioxide, and having the least damaging effect on the environment of all of the other fossil fuels. It is currently the cheapest option in terms of running costs. (see below) Natural gas is mains supplied, thus requiring no storage. The downside is that the supply may not be available to everyone. It is a legal requirement that a gas boiler is fitted by a CORGI registered engineer.

 Non-Return Valve

Aka Check Valve. Means a plumbing fitting designed to allow water flow in one direction only.

 OFTEC

The Oil Fired Technical Association. The organisation responsible for keeping track of professionals registered to fit oil fired appliances.

 Oil Powered Boiler

This is the most popular alternative to gas, used, for example, when location means no mains gas supply is available. Oil is not quite the cheapest alternative, but is a competitive option, although prices can change seasonally and vary with location. Oil is not the cleanest fuel and can contribute to acid rain amongst other environmental effects. The use of oil requires a storage tank. OFTEC registered engineers are most suitable for fitting oil boilers, although unlike gas this is not a legal requirement.

 Olive

Is the component in a Compression Fitting that provides the mechanical seal.

 One-Pipe System

Where the radiators are run in series, with the flow in and return out on the same pipe.

 Open Flue

Open Flue (or Chimney Flue). The air is drawn in from the room containing the boiler. The flue maybe driven by the air-flow or by a fan. These are most common in Back Boilers placed in an existing fireplace.

 Open Safety-Vent Pipe

Is the part of a Conventional Tank Fed Unpressurised Central Heating System that allows any pressure build up to be safely discharged to the atmosphere.

 Open-Vented System

Is a conventional central heating system which is un-pressurised and tank fed.

 Outlet Valve

Isolation device to control substances leaving an appliance.

 Overflow Pipe

A device fitted to a tank to safely discharge surplus water.

 Panel Heating

A method of heating involving the installation of the heating units (pipe coils) in the walls, floor or ceiling of the room.

 Panel Radiators

A heating unit placed on, or flush with, a flat wall surface and intended to function as a Radiator.

 Perforated Panel

This is a panel that is usually fitted across the front of a cabinet to dissipate the heat and add to the unit's appearance.

 Pilot Light

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.

 Pipe Joints

The connection point between two pipes, or a pipe and a component.

 Pitched Roof

A pitched roof is a roof with two or more slopes at more than 10 degrees to the meeting point.

 Porous

Surfaces that have tiny openings which allow liquid to be absorbed, or to pass through.

 Power Flushing

Power flushing is a process where the radiators and the connecting pipes are cleared in situ - being flushed! On completion your central heating will be repaired to optimum efficiency.

 Pressure Gauge

This is a gadget to tell the pressure of the water in the system pipe work.

 Pressure Jet Burner

The type of burner commonly used on all modern boilers and a number of cookers. Oil is injected, via a nozzle, into an airstream created by a fan. The oil is then vaporised and ignited by a spark.

 Pressure System

A water heating system for hot water to baths and basins which is sealed. Instead of the vent found in a header tank, a pressure vessel controls pressure. The advantage is that the pressure is high and so good for showers. Current Building Regulations require that if fitting this system, the details are submitted as a formal application for approval.

 Pressure Vessel

Is a hot water storage container usually at water mains pressure.

 Primary Heat Exchanger

Main Heat Exchanger in a boiler, usually serves the Radiator system.

 Programmer

A mechanical, electrical, or combination, device incorporating a timer that can be pre-set to enable a Central Heating System, to turn on at desired times.

 Pump

A device used to circulate water around the central heating system. Apart from primary pumps, pumps are generally not needed, as gravity will allow the water to circulate.

 Pump Impeller

Is the part of a Circulating Pump that drives the water.

 Pump Outlet

Is the water port on the Circulating Pump the water flows out from.

 Radiator

Transfers the heat from the hot water to the rooms.

 Radiator Valves

Used to control and isolate the water flow and return on a Radiator

 Relay

An electrical component, often found on the "PCB" used to switch secondary equipment such as Water Pumps, Gas Valves, and Flue Fans.

 Remote Acting Fire Valve

A valve fitted in the oil line external to the building which incorporates the sensor that is located inside the boiler casing so as to shut off the oil supply to the building externally in case of a fire or overheat at the appliance.

 Room Sealed Flues

By far the most common flues to find on a modern boiler. Boilers with a room sealed fanned flue can only be fitted to an outside wall. A double skinned pipe draws air in from outside and feeds waste gases back out again. In this situation flue gases cannot escape directly back into the room, and is therefore a safer option. Room sealed flues can operate through the natural draught of the air, or may be fan assisted to allow for longer flue runs.

 Roomstat

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.

 RSF

Room Sealed Flue. The flue is made of a double skinned pipe where fresh air from outside a property is drawn in through one section of the pipe and exhausted through the second.

 Safety Valve

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

 Scale

Scale builds-up due to Hard Water. You can treat the system with a descaler. Drain, flush and refill the system afterwards.

 SEDBUK Rating

The annual average efficiency rating of a piece of equipment on the SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) scale, ranging from A (highest) to G.

 Shank

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

 Sight Gauge

A transparent tube fitted in the outer pipe close to the tank and run vertically up to just above the highest part of the tank. Where the tube joins the draw off pipe there is a push bottom valve which when depressed enables oil to rise up the tube to the same level as the oil in the tank.

 Sludge

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

 Small-Bore Copper

General term to identify 15mm and 22mm pipe.

 Solid-Fuel Boiler

Any fuel that is not a liquid or gas, i.e., coal, wood, anthracite, etc.

 Standard Efficiency

Standard Efficiency boilers are available for traditional or combination systems. They operate at lower efficiencies than condensing boilers, but the initial purchase cost is less than High Efficiency (Condensing) models. New leglislation, introduced in April 2005 in England and Wales, strictly controls the number of homes that can be fitted with Standard Efficiency boilers.

 Standard Universal Backplate

A mounting plate fixing for a component.

 Stopcock

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

 Storage Vessel & Heating Vessel

Water storage tanks, usually located within the loft.

 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.

 System Boilers

System boilers, or 'Sealed System' boilers, are used in traditional system with a sealed radiator circuit. They have the expansion chamber included in the set or will have the components built in. For this reason some system boilers are larger than other types, and are best for homes where hot water demand is high.

 Temperature Pressure Relief Valve

A horizontal lever-like valve located near the top of a boiler at the water outlet joint.

 Thermostat

A device which switches heating control equipment on and off according to the temperature which has been set by the user.

 Thermostatic Radiator Valves

Non electric valves with regulate water flow through a radiator in accordance with the amount of heat required to maintain a pre set temperature in a room.

 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 to suit your lifestyle ensuring that the heating is not on while you are out or sleep.

 Traditional Boiler System

Traditional boilers are used to heat the radiators, as well as the domestic hot water that is held in a cylinder, usually located in an airing cupboard. This type of system is best if there is a high demand for hot water since the storage tank can absorb the impact of several hot water outlets being used at one time. Traditional boilers can be an advantage over Combination Systems if the mains pressure is too low to produce a decent flowrate at an outlet in the property.

 Trapped Air

If your Radiators or heating system seem to be making a noise then it may mean that there is air trapped somewhere, most commonly in the Radiators, which can be fixed by bleeding them. Read simple steps now to Bleed Your Radiator

 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.

 Valve

A mechanical device that regulates the flow of fluids by opening, closing or partially obstructing various passageways.

 Vaporising Burner

A type of burner often used in cookers and room heaters, which burns the oil by heating it so that vapour is given of to maintain a flame. Silent in operation

 Ventilator or Ventilation

An adequate air supply for heating appliances which use gas, oil or coal as their fuel requires them in order to burn correctly.

 Wall Mounted Boiler

Wall Mounted boilers are generally smaller and generally than floor standing boilers. They are typically more compact and in some instances may even be small enough to be positioned inside a wall mounted kitchen unit.

 Washer

A thin plate (typically disc-shaped) with a hole in the middle that is used to seal or shut off the flow of liquid or gas.

 Wet Central Heating

A heating system that uses water to carry the heat energy.

 Zone Valve

A zone valve is 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.

 Zoning

Providing separate space heating control for different parts of a building.