How does a system boiler work?

A system boiler, or sealed system, is a great option if you have more than one bathroom or your household has a high demand for hot water.

 

How does a system boiler work?

 

A system boiler contains all the major components of the heating system, including the pump and expansion vessel, which means installation is quick, neat and efficient. The boiler heats the water in a hot water storage cylinder, which in turn heats the water in the central heating system via a coiled heat exchanger and provides hot water to taps and showers.

 

Do I need a system or combi boiler?

 

If you have a high demand for hot water, for example, if you have more than one bathroom or shower room, a system boiler may be the perfect choice for you.

 

Will I need a separate expansion tank in the loft?

 

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.

 

Can system boilers supply several taps at once?

 

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

Our System Boilers

Our System Boiler heats up water in a sealed hot water cylinder, usually found in the airing cupboard, for hot water taps around the home.

Related FAQs

How do I know if I've got sludge in my central heating system?

If you notice your radiators are hot at the top but cold at the bottom, or need to bleed your radiators more often, then you may have sludge built up in your system. 

What should my boiler pressure be set at?

A safe level for your boiler pressure should be between 1.0 and 2.0 bar. Watch this video to learn how. 

Should I turn off my boiler in the summer?

In Summer, you might be tempted to switch off your boiler to save money. However, this can be inefficient and expensive. Instead, you should consider setting your boiler to only heat your water.

What is the Boiler Upgrade Scheme?

The Boiler Upgrade Scheme is a Government grant of £7,500 to support with the upfront costs of installing low carbon heating systems, such as an air source heat pump, subject to eligibility. A temporary uplift of £1,500 was also introduced in July 2026 to provide additional support for off-grid property owners.

Does my boiler filter need cleaning?

Your filter should be cleaned during your boiler’s annual service. This will prevent sludge building up in your system. Some filters come with an app that can warn you when they filter needs to be cleaned, so that you can arrange for your installer to visit before it gets too full.

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