Deciding which boiler to go for is a big decision and one which you’ll be living with for at least the next fifteen to twenty years, so you’ll want to get it right! 

One of the first decisions you will have to make is deciding on the type of boiler... and you may already have narrowed that down to a system boiler or a combi.

So, in this blog, we’re going to break down the difference between these two types of boilers and provide the  pros and cons of each to help you come to the right choice for your home.

What is a system boiler?

System boilers take cold water from the mains supply, where it’s then heated by the heat exchanger (which transfers the energy from the gas to the water). The hot water is then moved to a storage cylinder where it’s kept hot until you need it. The heating system is within the boiler system, and that’s where this type of boiler gets its name from.

And when you need the hot water, it’s then pulled from the tank. NOTE: a system boiler does need a cylinder to store the water which has been heated, but it doesn’t need a cold-water tank like conventional boilers.

What is a combi boiler?

A combi boiler is a highly efficient single unit that provides hot water for the water supply and the heating. This type of boiler takes water from the mains and heats it on demand whenever the tap or heating is turned on - meaning there’s no need for a storage cylinder.

The combination boiler gets its name because there’s the combination of two tasks, heating and hot water, all undertaken within the one boiler. And because there’s no need to pre-heat the water and then store it, the combi boiler is very cost effective. For other pros to this type of boiler, see below!

To find out more about combi boilers you can see our blog article "what exactly is a combi boiler and what does it do".

Pros and cons of a system boiler

So, let’s have a look at some of the pros of having a system boiler in your home:

• If you need hot water from several outlets at the same time, then a system boiler can cope with that level of demand as the water is already heated and ready to be used by all.
• The system boiler takes up less space than a traditional boiler because it takes water directly from the water supply (meaning it doesn’t need a cold-water tank - winner!).
• If you’re looking for hot water as soon as you turn the tap, then a system boiler can pretty much do that. That’s because a pump is built into the system, allowing the fast delivery of already heated water.
• And lastly, system boilers are compatible with solar panels that can generate power to heat the water in the hot water tank.

Sounds good, right? Now for the cons:

• If you suddenly need a lot of hot water, then you may use all the stored water and then have to wait until it heats up more.
• As the water needs to heat up in advance to when you want to use it, you’ll need to programme a timer for when is best for you. If your plans change, you may find yourself without some hot water.
• If you don’t have much space in your home, then you may struggle to find room for the hot water tank associated with this type of boiler.
• Once the hot water enters the cylinder, the temperature will begin to drop. This means that it’s essential that the cylinder is well insulated to prevent too much loss of heat - which then affects the boiler’s efficiency.
• There's more things that can go wrong with a system boiler so higher maintenance costs are a major con. However, you can reduce these costs by taking out a boiler cover plan. We recommend you do this!
• And finally, a system boiler is unlikely to be suitable for a home where there is a water supply with low pressure, or an older radiator system that may not cope with the higher pressure that comes with a system boiler.

Pros and cons of a combi boiler

Now let’s take a look at the pros of a combi boiler:

• If you need hot water on demand, then the combi boiler is a great fit for your household. While you need to wait for the system boiler to heat and then store the water, the combi heats the water once you turn on the hot water tap.
• They are highly efficient - in fact, there’s a requirement for all new combi installations to have an efficiency rating of at least 92%. This is great news as the energy bills will be much lower with a combi boiler, and you’ll be reducing your carbon footprint in the process too.
• It's easy to install and with no need to fit hot water cylinders, the boiler installation is much quicker with a combi boiler ... saving time and money (WINNER!).
• As the water is coming from the mains, you’ll have high-pressure hot water - though that does depend on the water pressure coming into your home to begin with.
• And finally, with just a single unit to find room for, combI boilers are a great choice for when space is limited.

So now you know all the pros of a combi boiler... here are the not so great things about them:

• A combi boiler will struggle to cope with a high demand for hot water. So, if you have the washing machine on while someone has a shower, then the water may suddenly go cold for one of those outputs... NOT IDEAL AT ALL! If you have more than one bathroom, then a combi will probably not be able to meet your hot water needs so definitely consider that.
• You will have to be a little patient with this type of boiler as once you turn on the hot water tap, the supply needs to be heated and then it’ll be sent to the tap. Now it is only a matter of a few seconds, but it’s not the speed of delivery that you’ll get from a system boiler.
• A combi boiler needs water to come from the mains at a high pressure. If the pressure is low, then the water coming from the taps will also be at a very low pressure which is frustrating.
• If your home has an older plumbing system, it may not be able to cope with the high pressure water flowing from a combi boiler, so it's important you check if your new boiler will require new pipes.

So which boiler is for you - system or combi?

Deciding on the right boiler for your home isn’t always an easy task but getting it wrong can mean that you’re not able to get the hot water and heating needed or that you pay more than you have to.

Finding a winner between system and combi boilers simply comes down to the hot water demands of your home.

For smaller homes with 1 bathroom, there's no better choice than a combi boiler. You'll be supplied with the instant access to hot water you need, from a highly efficient unit that should help you to save money on your energy bills.

But as beneficial as combi boilers are, they're unable to supply a strong supply of water to more than one tap, bath or shower at a time. So, for that reason, if you have two or more bathrooms then you should install a system boiler.

There are of course more than two types of boilers, and we have a full comparison of the different types of boilers on our Boiler Types page.

For any help or guidance, contact us HERE or give us a call on 01604 372395.