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Boiler Jargon Buster

Finding loads of weird words and phrases when looking for your new boiler, don't worry we've put together a handy boiler glossary for you



A device that controls the temperature of the water in the cylinder. It should be set to at least 60 degrees, in order to prevent legionnaires' disease.


Known for its high-quality boilers and adherence to stringent environmental regulations, Alpha is an internationally recognized boiler design and manufacturing company with a wide range of budget friendly, energy efficient boilers to choose from.



A closed vessel in which water or other fluid is heated. The heated fluid or steam is used to power machinery or for heating purposes.

British Thermal Unit (BTU)

A unit of heat energy that is used to describe the heating capacity of a boiler.


A device that mixes fuel and air and ignites the mixture in the combustion chamber.


Chemical Flush

The process of cleaning the interior surfaces of a boiler system using chemicals to remove mineral deposits, rust, and other debris that can accumulate over time.

Circulating Pump

A pump that circulates the water through the boiler and the heating system.

Compact Boiler

A boiler that is designed to take up less space than traditional boilers while still providing efficient heating.

Combi Boiler

A combi boiler, short for combination, is a type of heating system that provides both hot water and central heating from a single unit.

Combustion Efficiency

A measure of how completely the fuel is burned in the combustion chamber. It is expressed as a percentage.

Combustion Chamber

The area of the boiler where fuel is burned to produce heat.

Condensing Boiler

Condensing boilers uses condensing technology to make better use of the heat it generates - all modern boilers now use this technology.

Diverter Valve

A device that diverts the primary flow of hot water to either the heating system or the hot water cylinder.

Draft Regulator

A device that controls the air flow into the combustion chamber.

Electric Boiler

An electric boiler is simply a boiler that utilises electricity to heat water and heating systems.

Efficiency Rating

A measure of how effectively the boiler converts fuel into heat. It is expressed as a percentage.

Expansion Tank

A tank that allows for the expansion and contraction of the water in the heating system as it heats up and cools down.


Flow Rate

Flow rate is a unit to measure how much water your boiler can send to your taps or showers.


A duct or pipe that carries exhaust gases from the combustion chamber to the outside.

Fuel Source

The type of fuel that the boiler uses, such as natural gas, propane, oil, or electricity.


A boiler filter is a device that is installed into the heating system that traps impurities and debris from the circulating water or air, preventing damage to the boiler and other components in the system.



A distinguished UK-based boiler manufacturer with a legacy spanning over 75 years. Glow-Worm is celebrated for its energy-efficient boilers that seamlessly blend performance, quality, and value.


A boiler gasket is a mechanical seal that fills the space between two or more close surfaces in a boiler system to prevent the leakage of fluids or gases under high temperatures of compression.

Gas Safe Register

The gas safe register is the official register of gas engineers who are qualified to work safely and legally on gas appliances in the UK, Isle of man, and Guernsey.


Heat Exchanger

A device that transfers heat from the combustion gases to the water in the boiler.

Heating Controls

Heating controls are advanced controls that allow for a precise temperature and pressure regulation, remote monitoring, programming and energy efficiency operation.

Heat Only Boiler

A heat-only boiler, commonly referred to as a ‘regular’ boiler, requires a tank in the loft and a cylinder, usually in the airing cupboard. Heat-only boilers are typically found in larger properties as they can effectively meet the demand for hot water and heating across multiple taps, showerheads and radiators.



A leading name in the heating industry, Ideal Heating offers a comprehensive range of gas boiler systems tailored to fit homes of all sizes. From combi boilers suitable for smaller households to system and heat-only boilers designed for homes with multiple bathrooms.


Otherwise known as a pilot light, is a device that provides the initial flame or spark to ignite the fuel in a boilers combustion chamber, allowing it to heat the water or air in the system.


Boiler insulation is a layer of material or coating that is applied to the outer surface of a boiler to reduce heat loss and improve its energy efficiency.




kW refers to the thermal output of a boiler, which indicates the amount of heat energy it can generate per unit time, measured in Kilowatts (kW).


LPG Boiler

A LPG boiler is a boiler that uses propane or butane gas as its fuel source to heat water or air throughout a home.


Mains Water Supply

A boilers mains water supply refers to a plumbing system that connects a boiler directly to the main water supply of the building, providing a constant supply of fresh water for the boiler to heat and distribute.



A pioneer in high-efficiency condensing technology, Navien offers state-of-the-art boilers that cater to both small and large homes. With advanced features like Wi-Fi compatibility and a sleek wall-hung design, Navien boilers not only ensure optimal heating but also promote environmental sustainability by reducing greenhouse gas emissions.


Open Flue Boilers

Consisting of a pipe to carry combustion gases from the appliance, whilst fresh air enters the appliance via the casing. This means that, for safe operation, additional air vents are required in the room where the appliance is installed to re-supply fresh air.


Pressure Release Valve

A safety device that automatically releases pressure from the boiler if it becomes too high.

Pilot Light

A flame that lights the gas which is provided by the main burner, a small amount of gas is released from the gas pipe, meaning that the flame lights the gas and it permanently burns.


A reputable name in the heating industry, Potterton has been providing reliable boiler solutions for many years. Currently, Potterton products are supported by Baxi, another esteemed boiler manufacturer, ensuring that customers receive top-notch service and quality products.


Award-winning boilers, installed from tomorrow

Collection of two white and one black Worcester Bosch Greenstar 8000 Life boilers supplied by Padly



Boiler relocation involves the task of moving and lifting the boiler to be installed in a different location or different place within the home.


System Boiler

System boilers are self-contained units which contain many of the major heating and hot water components your home requires all compact into your cupboard. They don't require a cold-water tank or expansion tanks and are therefore ideal for homes with limited space – or homes looking to make the most out of loft space.

Solar Connector

A boiler solar connector is a component that connects a solar thermal system, typically consisting of solar panels, to a boiler or other heating system to supplement or replace a conventional fuel source with solar energy.

Smart Home Meter

A smart home meter is a device that measures and record energy usage and communicates the data wirelessly ot a smart home system, allowing homeowners to monitor and control their heating remotely, optimize energy efficiency and potentially save on energy bills.

Stop Tap

A boiler stop tap is a type of plumbing fitting used to connect a stop tap or isolation valve, allowing for easy maintenance or repairs by shutting off the water supply to the boiler without affecting the rest of the building's water supply.



A thermostatic radiator valve is a plumbing fitting that connects to a radiator allowing the valve to regulate the flow of hot water through the radiator and adjust the temperature according to the desired room temperature setting.


A device that controls the temperature in a building by turning the heating system on or off.




Viessmann has been pioneering advanced heating solutions since 1917. Offering a vast array of products, from energy-efficient condensing boilers to innovative solar thermal systems, Viessmann combines cutting-edge technology with sustainability, ensuring top-tier performance and eco-friendliness for both residential and commercial applications.


Waste Heat

Boiler waste heat refers to the excess heat energy generated by a boiler that is not utilized for its intended purpose, such as heating water, and is instead lost to the environment through the flue or other means, resulting in reduced energy efficiency and increased operating costs.

Worcester Bosch

A cornerstone in the UK heating market, Worcester Bosch, often simply referred to as Worcester, has been delivering top-tier heating and hot water products for decades. With a reputation for quality and reliability, Worcester Bosch remains a preferred choice for many homeowners and professionals.