Combi boilers (combination boilers) have quickly become one of the most popular types of boilers in the UK thanks to their ability to heat water on demand without the need for a hot water tank. Their name refers to the fact that they can provide both heating and hot water for your home when required.

If you’re considering replacing your conventional boiler with a combi, you may be wondering what the pros and cons are of this type of system. Ultimately, whether this system will work for you depends on the size of your home, the number of radiators and bathrooms you have, and the demand for hot water. Use the pros and cons below to help you decide whether you should change your boiler for a combi system.

Pros of a combi boiler

  • Very efficient
  • Compact
  • Instant hot water that’s always available
  • Easy to install
  • Save money on your bills (compared to an old conventional boiler)
  • No cold water tank

Very efficient

Around 55 per cent of your annual energy spend goes towards heating your home. This means that having an energy efficient boiler is extremely important. All new combi boilers that are installed in the UK need to be condensing and will have an efficiency rating of 90-94 per cent, so you’ll have a warmer home for less energy usage.

Compact

Combi boilers can be more compact. A conventional system may need a hot water cylinder, with a combi you don’t need a hot water cylinder alongside the boiler. This makes combis ideal for installation in a loft, utility or even in a kitchen cupboard. Some designs can incorporate a tank which allows for greater hot water flow rates in homes with a higher hot water demand or multiple water outlets.

Instant hot water when you need it

If you currently have a conventional boiler system, there may have been many instances where you run out of hot water. This is because when the boiler is programmed to turn on, it will heat your home as well as a large volume of water. This hot water is then stored in a large insulated tank that keeps the water warm for a few hours, making it available when you need to run a bath or wash the dishes. However, these tanks can only store so much hot water and once it has been used up, you would need to turn your boiler back on and wait a while for the tank to refill.

With a combi boiler system, this isn’t an issue. Instead of having a tank, the boiler can heat water as and when you need it, meaning you’ll never run out of hot water again. 

Easy to install

A combi boiler might be much easier to install than a conventional boiler because these models have fewer external parts. Whereas a conventional system will need to have a water tank installed as well, a combi boiler doesn’t need one of these. Not only does this mean your boiler can be installed much faster, but it may cost less too. 

Save money on your bills

A combi boiler might be much easier to install than a conventional boiler because these models have fewer external parts. Whereas a conventional system will need to have a water tank installed as well, a combi boiler doesn’t need one of these. Not only does this mean your boiler can be installed much faster, but it may cost less too. 

No cold water tank

Not only do conventional boilers have a hot water cylinder to store the heated water, they may also have a cold feed tank. This is generally located in the loft. The cold tank is filled with water from the mains which supplies the cylinder. As a combi boiler takes in water directly from the mains when it’s needed, there’s no requirement for a cold water tank, saving even more space in your home. 

Cons of a combi boiler

While combi boilers have a lot of benefits, there are still some things that they aren’t able to do as well as a conventional system. For example, a combi boiler:

  • Relies on good mains pressure
  • Doesn’t have an immersion heater
  • Doesn’t work with power showers
  • Doesn’t allow you to use multiple hot water appliances at once, although other combi possibilities are available as mentioned earlier in the article.

Relies on good mains pressure

Many conventional systems rely on gravity to work effectively. This is why the tank must be located as high up as possible (generally in the loft). However, a combi boiler takes its water in directly via the mains. If your mains supply has poor pressure, your taps and showerheads won’t have much pressure either. Before having a combi boiler installed, it’s a good idea to check your mains pressure. Although check with the installer for ways around this, for example booster pumps.

No immersion heater

Unlike conventional boiler systems, combi boilers don’t have an immersion heater. This means that, if your boiler was to break down, there is no backup system so you would be left completely without heating or hot water until the boiler is repaired. 

They don’t work with power showers

Many homes in the UK now have power showers. These are showers that have separate pumps, making for excellent water pressure. As a combi boiler uses mains water pressure, as discussed above, you can’t have a power shower with this kind of system. 

You can’t run multiple appliances at the same time

Finally, a combi boiler may not be able to cope if your home is large with multiple bathrooms. While one hot tap is running, you wouldn’t be able to turn on another one without the first one losing pressure or turning cold. This is because the combi boiler can only supply a certain amount of hot water at a time, whereas a conventional boiler can provide lots of water to different appliances thanks to the hot water cylinder. If you have a large home with multiple bathrooms, you may prefer to stick to your conventional system, however some combi boiler systems are available work around this issue by having a small tank placed internally, such as the Vitodens 111.

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