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Frequently asked questions about system boilers

Q. How much will I save by installing a new system boiler?

A. According to the Energy Saving Trust, you could save up to £310 a year by replacing an old, standard efficiency boiler. 

Check our Efficiency Calculator to see how much you could save.

Q. How do system boilers work?

A. The pump and expansion vessel, major components of the heating and hot water system, are built into a system boiler, which means that installation is quicker, neater, easier and more efficient.

The system boiler pumps hot water through the heating system to the radiators and to the hot water storage cylinder.

Q. How do I know if I need a system or combi boiler?

 A. If you have a high demand for hot water, for example if you have more than one bathroom or shower room, a system boiler maybe be the perfect choice for you. If you're not sure which type of boiler is best for your needs, try our product selector tool.

Q. Will I need a separate expansion tank in the loft?

A. There is no need for a feed and expansion cistern in the loft if you have a pressurised unvented hot water storage cylinder. If you have an open vented hot water cylinder, you will need a cold water storage cistern in the loft.

Q. Will I still need a separate pump with a sealed system boiler?

A. You do not need to have a separate pump because it is already built into the boiler.

Q. Can system boilers supply multiple outlets simultaneously?

A. A system boiler is perfect for homes with multiple bathrooms: hot water is provided by a storage cylinder, such as the Megaflo eco cylinder, so no matter how many taps you turn on, water will not run cold elsewhere in the house.

Q. Are system boilers economical to run?

A. By pumping hot water straight to the radiators and hot water cylinder a system boiler reduces the amount of time it takes for the property to heat up, thus reducing running costs. Wide modulation ranges ensure smooth operation, fewer ignitions, greater reliability and lower fuel bills.

System boilers are also compatible with solar thermal domestic hot water systems, like Baxi Solarflo and the Megaflo eco solar cylinder.

Q. What sizes do gas system boilers come in?

A. Baxi system boilers are available in outputs from 12 to 32 kW to meet the heating and hot water requirements of any size property.

Q. Can I get a system boiler if I have LPG?

A. Yes, the Baxi Megaflo System Compact GA boiler works with both natural gas and LPG. 

Q. What is SEDBUK? 

A. SEDBUK is the national standard for energy performance for heating appliances. SEDBUK stands for 'Seasonal Efficiency of a Domestic Boiler in the UK', and is designed to provide a fair comparison of the energy performance of different boilers.

SEDBUK 2005 ratings are shown on labels as A-G, similar to those found on refrigerators and washing machines, where A is at least 90% efficient. This seasonal efficiency method was superseded by SEDBUK 2009, where the boiler efficiency is shown as an annual efficiency percentage.

All boilers installed in the UK from 6th April 2011 must be greater than 88% SEDBUK (2009) or greater than 90% SEDBUK (2005).

Q. Can system boilers be made even more energy efficient?

A. Additional savings of £70 and 280 kg carbon dioxide a year can be achieved by installing a room thermostat, according to Energy Saving Trust.

The Baxi EcoBlue System and the Baxi Megaflo System Compact GA are compatible with the Multifit GasSaver GS1c, and can save up to 37% of the gas used to heat hot water annually. Test conducted by independent scientific test house TNO, based on an average household's consumption of 100 litres of hot water per day.

The GasSaver uses hot exhaust gases from boiler combustion to pre-heat incoming water to the boiler, saving energy and money.

Q. Who can install a new system boiler?

A. All gas work carried out in your home should be done by a Gas Safe registered engineer. The Gas Safe Register is the official list of gas engineers who are registered to work safely and legally on boilers, cookers, fires and all other gas appliances.

Gas work includes:

• installing, repairing or servicing a gas boiler

• installing or repairing a gas fire, gas cooker or hob

 You can find a local Gas Safe registered installer by using Find an Installer.

Q. How often should I get my system boiler serviced?

A. Your boiler should be serviced annually by a Gas Safe registered installer in order to check that it is operating safely and at peak efficiency. An annual service is also a requirement of your boiler's warranty.

Baxi Customer Support can provide servicing and support for all of our heating products, while the product is both in and out of warranty.


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Our series of FAQs, technical advice articles and 'How to...' videos are designed to help you understand your boiler, provide helpful tips and even save you money.

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