Home Improvement

How Does a Combi Boiler Work – Inside The UK’s Most Common Boiler

The combination boiler is the most popular type of boiler in the UK and for good reason. Its simplistic controls, compact size and temperature control are almost second to none, so it’s no wonder that many homes across the country now have a combi installed.

But a question arises; how does a combi boiler work? Stick with us for a definitive answer to that question.

So if you:

  • Have a combi boiler, or are looking to install one;
  • Want to know how a combi boiler works;
  • Are wondering about the positives and drawbacks of combi boilers;

Then read on!

How does a combination boiler work?

Part of the answer is in the name of the boiler. Combi boilers join both central heating and water heating boilers into one comprehensive unit. Combi boilers work by using two heat exchangers. The primary heat exchanger heats and reheats water that flows through a property’s pipes and radiators (central heating). The secondary exchanger heats water supplied through the mains, which will then travel to your taps and provide hot water.

Primary heat exchanger

The primary heat exchanger will maintain a temperature that is set on a room’s thermostat. If the temperature drops below the set threshold, the boiler will fire up and begin heating water that will be sent through pipes into the radiators. From the radiator, it is sent back to the boiler where it is reheated again in a cycle.

As you can imagine, this results in a lot of dirty water. Thankfully, this isn’t the water that will travel to your taps.

Secondary heat exchanger

The secondary heat exchanger uses water from the main water line. When you open your hot tap, water toggles a paddle called the dabble pressure switch. This turns on the burner and a pump at the bottom of the boiler. This pumps water from the burner (used in the primary heat exchanger) to pipes within the secondary heat exchanger. The cold mains water is then heated through the heat exchanger and will then pass towards your taps.

You should keep in mind that combi boilers can’t use both exchangers at the same time. When the dabble switch is flicked, all heat will be diverted to the secondary, until the taps are closed.

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How does a combi differ from conventional boilers?

Though they function similarly to conventional boilers, combis differ vastly from their counterparts. Keep in mind, while combi boilers offer a range of benefits, they do have some drawbacks too and are usually suited to specific properties and needs.

Combi boilers advantages

Let’s start with the pros of having a combi boiler. 

  • Energy-efficient – In comparison to conventional boilers, combis can be very efficient. Most combis are fitted with a flue gas recovery system, which it uses to preheat cold water coming in from the mains. Conventional boilers expel these gases, wasting energy potential.
  • Fairly easy and quick installation – Because of their compact nature, combi boilers are relatively easy to install. They usually take around 4-6 hours to install, which is much less than a conventional boilers’ 1-3 days. This is because everything is in one case and you won’t need to install a water cylinder and tank for a combi to work.
  • Take up less space – Combis use mains water, so there is no need for a bulky water tank in the loft or airing cupboard. This makes them more suitable for smaller properties, where space is a top priority.
  • Heat up water quickly – Combis will supply you with hot water almost instantly, whereas a conventional boiler can take upwards of 30 minutes to deliver hot water.
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Combi boilers disadvantages

As mentioned before, combi boilers are more suitable for smaller homes, which means that they may not be the best choice for larger properties or families. The water flow may be impacted by having multiple users at one time, a problem that conventional boilers don’t have. Other combi boiler cons to consider are:

  • Hot water for one water draw – Combi boilers will only provide hot water for one water draw at a time. That means you won’t be able to use the hot tap in the kitchen sink and the shower at the same time if they’re hooked up to the same boiler. Conventional boilers can support many users at the same time, however.
  • Breakdowns mean no access to hot water – A major drawback is that when combi boilers break down, you get no access to heating or hot water. Conventional boilers however will still supply hot water to the property, even if the central heating is malfunctioning.
  • Need of good mains pressure – Combi boilers also require good mains pressure in order to work properly, meaning you might want to get your pressure tested before installing one. Also, because it can’t store hot water, if it malfunctions, you’ll be without both central heating and hot water.
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Is a combi suitable for my household?

It really depends on a number of factors. For smaller living spaces and homes with one bathroom, a combi can be perfect. As mentioned above, it runs on mains water, so you won’t need to make space for a large water tank. Plus, if you live by yourself, or one other person the water draw issue won’t be much of a problem.

Plus, combis are more energy efficient in comparison to conventional boilers. As they supply hot water on demand and won’t need to constantly heat and reheat a hot water tank, your energy bills can decrease by up to 40%.

Looking to install a combi boiler?

Fantastic Services can help you with a boiler installation service! We work with gas safe engineers who have the tools and experience to install any boiler. The engineers work on a flexible schedule, so you can book a time slot that will be perfect for you.

We also offer boiler cover plans, so that you are protected and insured from potential problems and breakdowns in the future. Plus, you get an annual boiler service every year as part of the plan, so you can make sure your boiler is in good working order.

So what are you waiting for? Book your boiler installation service today!

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  • Combi boilers do everything that a standard boiler does, in a small compact unit.
  • Combi boilers are energy and space-efficient and can provide hot water instantly.
  • While they are good for smaller properties, they might not be suited to larger living spaces.
  • Before choosing a combi boiler consider whether it would be suitable for your property.

We hope you found our article on combi boilers helpful! If you have any questions, consider leaving a comment with us below.

Image source: Radovan1 / Shutterstock

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