What is a heat only boiler?

Often seen as the standard way to heat your home, heat only boilers (also referred to as regular boilers) are ideal for homes with traditional central heating and hot water systems. 

Is your home suitable for a heat only boiler?

Does your home have multiple taps, showers and baths, often used at the same time? If so, a heat only boiler is likely to be perfect for your home.

Which homes are most suited for heat only boilers?

You may be recommended a heat only boiler if your home has an older radiator system that may not be able to support the high water pressure (which can cause leaks) produced by other types of boiler, such as system boilers. Secondly, if you also live in an area with particularly low water pressure, we’d tend to suggest a heat only boiler for your home. This means you can use water from a cold water storage tank to fill the cylinder rather than directly from the mains.

Why choose a heat only boiler?

Nevertheless, heat only boilers are a popular choice because they’re able to generate lots of hot water for different taps at the same time and are generally the most powerful of the main boiler types. Read our guide below to learn more about how heat only boilers work, their benefits and whether your home is suitable for one.

Hot water from multiple taps

Hot water is heated and stored in a cylinder, ready to use when needed and you can get hot water via multiple taps and showers at the same time.

Ideal for low water pressure homes

As the water pressure is created by gravity from the tanks in your loft, they’re ideal for homes with lower mains water pressure.

Use solar power

Heat only boilers can use solar energy to heat water, reducing your energy usage and maybe even saving money on utility bills.


Our award-winning Worcester Greenstar range of heat only boilers is recommended by Which? so you can guarantee your boiler is of the highest quality.

What is a regular boiler?

Heat only boilers are also called regular, traditional and conventional boilers because they were historically the most common boiler type in UK 

How does a heat only boiler work?

Of all the types of boilers, heat only ones have the most separate components around your home which work together to produce hot water. This is why they’re suited to larger properties, particularly ones with lofts to fit the cold water tank. Installing heat only boilers can take longer than other types but benefit from being able to handle high demand for heating and hot water.

Open vented boilers

There are two different systems of heat only boilers. The first, open vented boilers have two tanks, a cold water tank and a Feed and Expansion (F&E) tank. They are normally kept in the loft, or the highest part of your home as they use gravity to produce water pressure.

How do open vented boilers work?

The cold water tank is filled with water from the mains supply and is then transferred to the hot water cylinder. From there, the coil in the cylinder warms the water and sends it to the radiators, taps and showers to be used.

The F&E tank tends to be smaller than the cold water tank and performs two jobs. Firstly, to release pressure in the hot water cylinder caused by water expansion as it heats up and also to feed this water back into the system (radiators, hot water cylinders) as it cools.

When hot water or heating is being used, the F&E tank will replace the water that’s been used or evaporated in the process. It is called ‘open vented’ due to a pipe that goes from the water cylinder and sits over the F&E tank. This pipe releases any pressure from hot water expansion to prevent damage or overheating.

How common are open vented boilers?

This style of boiler was the most popular in UK homes until the 1980s when the modern combi boiler became preferred. Despite this, open vented systems are still used today and remain the best setup for homes with higher heating and hot water demands.

How do sealed system boilers work?

A sealed system doesn’t have a F&E tank and instead has an expansion vessel that collects water as it heats and expands. In the event of overpressure, they also have a pressure relief valve that can release any surplus water.

Once the water cools, the expansion vessel sends water back into the system. To replace the water levels in the boiler system, a ‘filling loop’  is connected to the mains water pipework. When turned on, it connects to the mains water to ensure optimal water levels.

Which system is better?

Open vent systems are simpler with fewer fittings and parts. This usually means lower maintenance costs and it’s faster to replace than a sealed system. As these tanks are open to the atmosphere, oxidisation can happen which may lead to pipe erosion over the course of time. We recommend that you clean these tanks every so often to help prevent that.

Sealed systems take up less space and, because they’re sealed, are cleaner than open vented systems, where debris can enter. It’s also more energy-efficient as they don’t have F&E tanks which can have issues with heat loss. However, If you've got older radiators, it would be better to get an open vent system or consider replacing your radiators.

How much does a heat only boiler cost?

There's no fixed price for a heat only boiler, as it depends on how powerful you need it to be. You can get an online quote for a new boiler that’s perfect for your home in less than two minutes with our online tool. We can also email your quote to you, with your price fixed for 30 days.