These are the three main boiler types; a combi-boiler heats the water as required and is connected to the mains water supply. A System boiler works together with a hot water cylinder but may not need a tank as the system can be filled directly from the mains. Finally an open-vent system is a more traditional system usually found in older properties. This uses a separate hot-water cylinder or immersion heater and requires a tank to store cold water.

An acronym which stands for Seasonal Efficiency of Domestic Boilers in the UK. This is a database which provides a simple way of comparing the energy efficiency of different boilers.

Recent changes in the law mean that all new gas boilers fitted in the UK must be high-efficiency. A high efficiency boiler extracts more energy from the fuel making them up to 90% efficient. Standard efficiency boilers can waste over a third of the energy produced so upgrading your system could save you as much as 30% on heating and hot water bills as well as reduce your carbon footprint.

An adjustable valve connected to each radiator allowing you to regulate its temperature. TRV stands for Thermostatic Radiator Valve.

‘Combi’ is short for combination boiler. This type of boiler heats water as you draw it from the tap and provides central heating. It doesn’t need a cold water feed and expansion tank or a hot water cylinder because the boiler is connected directly to the water mains, meaning it only heats water as and when it is needed.

As you only have the combi boiler unit in this heating system, it can free up space for conversion, storage and living. Homes that need larger supplies of hot water are usually better suited to a system or open vent boiler with a hot water cylinder.

This is done to clean the system, clearing out sludge that has built up over time and may damage the boiler or cause it to be ineffective. A Power flush does come with some risk as any poor or damaged pipework may leak under the extra pressure.

A central heating system works under pressure, if this drops too low then the boiler may not fire. A drop in pressure may be caused by a leak so it’s a good idea to contact an engineer to find and fix the leak.

This is probably because there is air trapped in the system and you need to ‘bleed’ the radiators. You may also hear a bubbling noise when the heating is running. You can easily bleed a radiator yourself using a radiator key but be prepared to shut the valve immediately once the air is released, before the water shoots out. Have an old towel ready to protect yourself and your furnishings as any water which escapes could be dirty and hot. Once the radiators are bled, you may need to repressurise the system.

This is an internal part of the boiler which switches between the functions of heating and hot water. If this part malfunctions then you may find that you only have heating OR hot water, not both.

A boiler service will maintain the lifespan and efficiency of your boiler, potentially saving you money in energy bills and boiler breakdowns over the long-term. Just like a car it pays to keep your boiler in good working order and is also a condition of most boiler guarantees.

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