Heat only boilers, also known as conventional boilers, provide central heating to our homes and are installed in many UK properties built before the 1970s. Despite them being common household appliances, the workings of these boilers are still a bit of a mystery for many of us.

If your heating system has a cylinder and a pair of water tanks, most likely up in the loft, you have a heat only boiler. All of these pieces work together to provide all the hot water we need for our homes’ radiators, taps and showers. 

In this article, we’ll answer common questions, including how a heat only boiler works, explore their key benefits and ask what sort of properties they are best suited to.

How Does a Heat Only Boiler Work?

Heat only boiler models keep our homes warm and provide the hot water we need for our kitchens and bathrooms. Depending on whether you have an open-vented system or sealed system (see below), your heat only boiler will work hand in hand with several extra pieces of equipment:

The cold water tank is filled from the mains supply, which in turns feeds into the hot water cylinder. That’s where the water is warmed up by a heat exchanger inside your boiler, before it’s then used to supply your radiators, taps and showers with hot water.

A pump is used to send all of the hot water that’s produced through your central heating system, supplying your home’s radiators as well as any taps and showerheads.

Sealed and Open-Vented Heat Only Boilers

If you have an open-vented system, a feed and expansion tank will make sure the system’s water levels remain at the same level. It ensures any water lost through evaporation or leaking is replaced, as well as making sure that water expansion caused by heating doesn’t lead to a build-up of pressure.

A sealed system uses an expansion vessel rather than a feed and expansion tank. This might be built into the boiler or be a separate containment unit, and provides space to house water as it expands when the system is heating up.

What are the Benefits of a Heat Only Boiler?

If your home has a high demand for hot water, either because you have a lot of radiators or two or more bathrooms, a heat only boiler could be the right central heating solution for you. They can supply large amounts of hot water at the same time, whereas another model such as a combi boiler may struggle to keep up with the demand.

An additional positive of heat only boilers is that they deliver hot water through your central heating system using a pump, which means they aren’t under pressure. This means that if the area where you live doesn’t have high water pressure, this won’t stop a heat only boiler from working properly.

What Size Property is a Heat Only Boiler Best For?

Heat only boilers are best suited to large homes where a steady supply of hot water may be needed at the same time, such as a property with two bathrooms where several people all need to wash and shower in the morning.

If you have plenty of space to house your boiler, most likely in your loft, then a heat only boiler would be a great option. For an example of a modern, hard-wearing heat only boiler, take a look at the specs of the Ideal Logic+ Heat to see if it could be the right fit for your home.

Are There Any Drawbacks to a Heat Only Boiler?

A key point to be aware of when it comes to heat only boilers is that they can run out of hot water, because they draw water from a cylinder rather than directly from the mains.  Once all of the water from the cylinder has been used, it will need to refill with cold water and heat it to the temperature needed for our hot water taps and showerheads.

Another thing to consider is that if you don’t actually use a lot of hot water, a heat only boiler may not be the most efficient heating solution. The cylinder may heat up more water than you require to use, whereas a combi boiler will only provide the amount of water you need.

How Often Should I Service My Heat Only Boiler?

We always recommend that your boiler should be serviced at least once a year. These appliances play a huge part in keeping our homes warm and comfortable, so it’s important that we look after them for a whole range of reasons.

An annual service will leave you secure that your heat only boiler is working safely and efficiently to provide the hot water and heating you need, as well as making sure that it stays under warranty. It’s a quick and easy job to book a service for your Ideal boiler online.

Should I Replace My Heat Only Boiler with a Combi?

If your home has three bedrooms or less, one bathroom and one shower, it’s possible that a combi boiler could be a better option for you. Because it only uses the hot water you need rather than maintaining a constant supply, a combi would make a more efficient choice.

However, if you live in an older home with less modern radiators, they may not be equipped to cope with the high water pressure supplied by a combi or system boiler. To learn more about the benefits and drawbacks of combi boilers and system boilers take a look at our pages What is a Combi Boiler and What is a System Boiler.

For further advice on choosing which best boiler is the right pick for your household, why not try our quick and easy boiler selector tool?

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