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General boiler info

How Does a Heat Only Boiler Work?

All about heat only boilers 

Heat only boilers are also known as conventional, traditional, open vent or regular boilers. If you have an old heating system with a hot water cylinder and water tanks in the loft, it is likely you have a heat only boiler, and you can replace like for like. You would not have to change pipe work and remove the tanks and cylinder, so it should cost less. Remember, though, that you should always have a power flush carried out to clean the system, so that you are not fitting a new boiler onto pipework filled with sludge.

Here we explain how heat only boilers work and answer some frequently asked questions.

What are the benefits of heat only boilers?

  • As most traditional heating systems have a heat only boiler, it is easier to replace with a new high efficiency heat only boiler without too many pipework changes, keeping installation costs to a minimum
  • A good solution for homes requiring a large volume of stored hot water, such as homes with two or more bathrooms. Compatible with Heatrae Sadia vented hot water storage cylinders
  • Ideal for homes in areas that have low mains water pressure
  • Compatible with solar thermal hot water systems that use free energy from the sun to heat the water in the cylinder, helping to lower energy bills and reducing your carbon footprint

How does a heat only boiler work?

Heat only boilers are usually installed as part of an open vented system that has two water tanks – a water storage tank and a small feed and expansion tank – usually sited in the roof space of the house, and a hot water storage cylinder, usually installed in the airing cupboard.

Cold water from the storage tank is fed to the hot water storage cylinder and the boiler heats the water in the cylinder, providing hot water to taps throughout the house.

The second tank in the loft, the feed and expansion tank, maintains the correct level of water for the heating system and allows for the water expansion when the heating is switched on. A pump, usually also installed in the airing cupboard, circulates hot water through the heating system pipes to the radiators.

Showers, taps and baths can be drawn at the same time, but if all the hot water in the storage cylinder is used up, it will take a little time to reheat.

What output of boiler and size of cylinder will I need?

Your Gas Safe registered installer will do a site survey and find out your specific requirements. Then he can calculate the correct sizes for your system.

What are the heat only boilers in the Baxi range?

What other controls do I need with my heat only boiler?

Since the Building Regulations changed in April 2018 (commonly known as Boiler Plus), time and temperature controls are required for all boiler installations.

Who can install my new heat only boiler?

All gas installations must be carried out by a Gas Safe registered engineer. You can find your nearest Baxi Gas Safe registered installer using our Find an Installer tool.

How often should I have my heat only boiler serviced?

An annual service will keep your boiler working reliable and efficiently and check it is safe. It is also a requirement for keeping your boiler warranty valid. Your local Baxi installer can carry out the service for you or you can contact Baxi Customer Support to arrange for one of our engineers to visit.

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