Combi Boiler vs System Boiler: The Ultimate Debate

Combi Boiler vs System Boiler: The Ultimate Debate

combi boiler vs system boiler

Answering the combi boiler vs system boiler question isn’t as simple as picking the cheapest model. For most homeowners, multiple factors need to be considered before settling on a boiler unit that’s right for them. You’ll need to consider factors such as how much hot water you use, the size of your property, and whether you have space to accommodate a larger system. At first glance, combi boilers and system boilers can look identical. However, these two boiler types work differently.

For most people, the amount of hot water supplied will settle the debate about which to choose. Below, we’ll break down what you can expect from both system boilers and combi boilers. We’ll explore installation considerations and how well they’ll meet your hot water demands. 

Thinking about replacing your existing boiler? At Complete Plumbing Solutions, we’re your go-to provider for new system replacement, no matter what model you settle on.  

Getting a System Boiler 

If you live in a busy household with a high demand for hot water, a system boiler might be the best solution. However, there’s much to consider before settling on a system boiler. Below, we’ll explore the main advantages and applications of system boilers and their drawbacks. 


They’re a Compact Solution 

If you’re thinking about a gas boiler replacement, size might be a contributing factor. This is understandable. Traditional boiler models are fairly bulky, especially those with large tanks that are stored in lofts. These systems store cold water that is then distributed to your boiler before being heated and diverted elsewhere. 

System boilers are far more compact, drawing cold water directly from your main supply. There’s no compromise when it comes to hot water supply, but you do benefit from freeing up your loft space. This makes them an obvious choice for anyone looking to convert upper storeys into living space.  

The Best Choice for Homes With Several Bathrooms 

Do you have more than one bathroom? Even if you only have a compact ensuite alongside a family bathroom, your hot water needs are going to be high. As such, you’ll need a boiler that can deliver. A system boiler is an ideal solution for homes that are constantly running multiple hot taps and shower faucets at the same time. 

System boilers feature storage cylinders, providing you with a ready supply of hot water and no discernible loss of water flow. Inbuilt pumps also deliver quick response times, circulating hot water at rapid speed around your home.  

Compatible With Solar Panels 

If you’re looking for an eco-friendly solution, the combi boiler vs system boiler debate is an easy one to answer. Some system boilers can be combined with solar panel technology to help you slash your monthly energy expenditure.  

The Drawbacks of System Boilers 

Although they can free up loft space, system boilers aren’t as compact as combi models. This is largely down to the integrated pipework and the size of the water storage cylinder. It’s tempting to choose a smaller cylinder, but if you opt for something too small, you may find yourself waiting longer than you’d like for hot water.

How does a system boiler work? While the overall process is fairly fast, hot water isn’t always instantly available. If you’ve used more hot water than you usually do, the cylinder can take a while to refill. This may be an issue if you’re hosting overnight guests.  

Getting a Combi Boiler 

A combi gas boiler has many advantages over other boiler types. From hassle-free installation to cost-saving benefits, there are many reasons why combi boilers are such an attractive option for the average homeowner.  


A Low-Impact Option 

Combi boilers are incredibly compact. These systems don’t include any additional tanks or water storage cylinders, meaning they can be hidden away in a kitchen cupboard or utility room. If you live in an apartment or small family home, they’re a practical choice that won’t eat into the precious square footage. 

Incredibly Efficient 

For most people, energy efficiency will help settle the combi boiler vs system boiler conundrum. Today’s combi boilers will boast a minimum efficiency rating of 92%. This not only ensures a ready supply of hot water and a warm home but keeps your heating bills as low as possible.  

Easy to Install 

Because a combi boiler doesn’t include any cylinders or tanks, installation is fairly simple. Additionally, the cost of replacing gas boilers with a combi model is generally cheaper. A regular gas boiler service is relatively straightforward when compared to more complex models.  

Enjoy Hot Water All The Time 

As with system boilers, a combi boiler will draw cold water directly from your main supply. As such, you’ll enjoy hot water whenever you need it. You’ll also benefit from strong flow, although this can vary depending on the mains water pressure in your area.  


Unfortunately, combi boilers do struggle to meet incredibly high hot water demands. If your central heating system includes many radiators and your home has several bathrooms, even pressure isn’t a guarantee.

Combi boilers aren’t ideal for properties that suffer from low mains pressure. If you have an older property, you may also need to invest in pipe refits before a modern combi boiler can be installed. Older pipework won’t deliver the main pressure needed to get the most out of a combi boiler system.  

When Is a Combi Boiler Better Than a System Boiler? 

A modern combi boiler is a good choice for smaller sized homes and apartments. As well as being able to cope with your hot water demands, these compact boilers won’t take up too much space in small kitchens or utility cupboards.

However, a combi boiler is still worth considering if you live in a larger property. Even a two to three-bedroom property can be served well by a combi boiler. That being said, consider your hot water usage. If you’re using your central heating system throughout the day or you have more than one bathroom, a combi boiler might not cut it.  

When Is a System Boiler Better Than a Combi Boiler? 

The combi boiler vs system boiler debate is easier to solve if you live in a larger household with more intensive hot water needs. If you have more than one bathroom and at least three bedrooms, you’ll need a system that delivers hot water on demand. 

Combi Boiler vs System Boiler: Which Is Best for You? 

System boilers are compact and great for homes with bigger central heating systems and more than one bathroom. Some system boilers can also be combined with solar panel technology, helping you save on your energy bills. However, while you’ll be able to free up some of your loft space, that extra pipework and storage cylinder needs to go somewhere. While the hot water supply is fairly consistent, the more you use, the longer it will take for your cylinder to refill.

Combi boilers are easy to install and the best choice for smaller properties. The most compact of combi boilers can be hidden away in an unused cupboard. They’re also an efficient choice, helping you to stay on top of rising energy bills. While affordable, these boilers will struggle to meet the higher demand for hot water. They’re not always suitable for homes with multiple bathrooms and many bedrooms. If you suffer from low mains pressure, a combi boiler probably isn’t the way to go. 

Thinking About Replacing Your Boiler?

Is your central heating system struggling to keep your home warm? Are you tired of waiting around for hot water? It’s time to think about replacing your boiler with a more efficient one. At Complete Plumbing Solutions, we can help you make the right choice. 

Wondering how often you should service your boiler or how to flush radiators? As a plumber in Cork delivering 5-star service, we can also help with everything from power flushing to pump services and everything in between. Looking for a plumber in Mallow? We cater to domestic and commercial customers throughout County Cork.

Ready to say goodbye to an inefficient boiler? Get in touch today with all your combi boiler vs system boiler questions. Email us at [email protected] or drop us a call at (085) 169 4244.