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A small boiler fitted at the back of the hearth of an open fireplace or in a room heater to provide domestic hot water and sometimes to heat radiators within a dwelling.
A boiler is a box in which a controlled burn of fossil fuel is carried out and the heat produced is transferred to water.
This is the name given to a boiler that heats water instantaneously on opening a hot tap. There are no tanks in the loft and no storage cylinder. The water is fed from the mains so the water pressure is generally stronger.
All boilers have controls that allow you to adjust the water temperature and space heating temperature (thermostat). Other controls the boiler may have are a water pressure gauge and a digital or electro-mechanical timer.
Domestic Hot Water
As the water in the heating system gets hot it expands; in sealed systems the 'expansion vessel' (a small pressurised container) accommodates the extra volume.
Traditional heating system use two tanks that are usually found in the loft. One feeds fresh water to the hot water storage cylinder and the other one (usually smaller) maintains the correct level of water in the heating system. They also allow for expansion of the water in either when it gets hot - hence the name 'feed and expansion' tank.
Generally the term 'flow rates' is associated with combi boilers. It refers to how much water (usually measured in litres) can be heated as it flows though the pipes in a given time (usually per minute). A powerful boiler will heat more water therefore providing a better flow rate.
All boilers have some sort of flue system; there are typically two types:
A heat only boiler is a conventional boiler which works in conjunction with a hot water storage and cold water top up tanks to provide both central heating and hot water.
All high efficiency (HE) boilers are environmentally friendly and operate at up to 96% efficiency compared to standard boilers at around 80% efficiency. They recover heat that is normally lost to the atmosphere via the flue gases.
Depending on the model, your boiler may be wall mounted, floor standing or hidden away in a fireplace.
If your heating system has a feed and expansion tank, it's called 'open vented' hot water. A hot water storage cylinder may also be open vented.
The output ratings of boilers are measured in BTUs (British Thermal Units) or kW (kilowatts). A low output would be 30/60,000 BTUs (9 - 17kW). A high output would be 60/100/000 BTUs (17 - 29 kW). Your installer should choose the output best suited to the size of your heating system, the type of property and, in the case of a combination boiler, the amount of hot water you require.
If you have a sealed heating system there's no feed and expansion tank (see F&E tank) in the loft space. Instead it's filled with water via a temporary connection and expansion is accommodated by a special vessel, which may be inside the boiler (see also expansion vessel)
SEDBUK stands for Seasonal Efficiency of Domestic Boilers in the UK. It is the Government's boiler efficiency database and lists the SEDBUK ratings for all domestic boilers in the UK. For full details see http://www.sedbuk.com/.
The storage cylinder supplies hot water for domestic use and is heated by the boiler. As the hot water in the storage cylinder is used up it is refilled by the feed and expansion tank (see F&E tank).
A 'system' is the term used to describe the boiler and all of its components required to provide your home with heating and hot water
The term 'unvented' most commonly refers to cylinders able to store water at mains pressure, thus removing the need for a feed and expansion vessel. Therefore flow rates are usually far superior.
Wall Hung Boiler
The Potterton range of gas boilers includes Combi, System, Heat Only and Floor standing.
The Potterton Gold Combi 24 HE has been awarded a Best Buy by Which? magazine for two years running.
