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Combi Boiler vs. System Boiler – Which One Should You Get?


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Ever heard of a war cry that goes “Piping hot against pressure-powered”? No? Well, you’re about to, because we’re diving into the epic clash of the boiler titans – Combi vs. System! Choosing the right one under eco4 grants is like picking a side in a superhero movie, and trust me, both have their superpowers (and kryptonite).

So, which champion deserves a spot in your home heating kingdom? Let’s break down their strengths and weaknesses like a fearless reporter at the scene of a boiler brawl! But before that, it would be appropriate to let you know what these boilers are.

What is a Combi Boiler?

A combi boiler, also known as a combination boiler, is a small heating system that efficiently provides both warmth and hot water from a single unit. When you turn on the tap, it quickly heats up water directly from the mains, eliminating the need for a hot water storage cylinder or a cold water storage tank in the attic. This is especially useful for homes with limited space or minimal hot water needs.

What is a System Boiler?

A system boiler is commonly found in larger homes with a higher demand for heating and hot water. In contrast to combi boilers, which heat water instantly, system boilers come with a water cylinder, ensuring a continuous supply of hot water throughout the house.

Where Can We Install System and Combi Boilers?

Both combi boilers and system boilers can be used for both central heating and domestic hot water supply. Combi boilers can integrate with underfloor heating, although it might require adjustments like adding a two-port valve.

System boilers can also be used for underfloor heating installations, working alongside a separate hot water cylinder that provides the necessary heat. However, system boilers may require modifications such as adjusting the parameters of supply water and screed thickness or reshaping the layout of heating pipes to integrate with underfloor heating systems.

Combi vs System Boiler

Firstly, think of instant hot water. You want it hot and fresh, right? But how do you get it? Well, both combi and system boilers have different procedure to heat water. Moreover, both boilers take different time to provide this service. In the below lines, we’ll discuss this matter.

How system boiler heats water?

A system boiler has already a hot water tank.  So you can use hot water thinking it must be hot water, but sometimes it may not be. Although it may be true that system boiler always keeps hot water ready, but as mentioned it may not.

  • Pros: Great for big families or long showers. Always has hot water available.
  • Cons: Takes up more space, costs more to run (like the pizza delivery guy’s gas), and can run out of hot water if you’re too hungry.

How combi boiler heats water?

Combi boiler on the other hand, provides hot water as per demand. So the water is always fresh and never runs out.

  • Pros: Because this is smaller and saves energy, you only pay for what you use.
  • Cons: Might not be fast enough for big families or long showers. For the same reason, it takes longer to get hot water in the furthest rooms.

So, which one is better?

It depends! If you’re a pizza party animal, a system boiler might be your best friend. But if you’re a solo snacker who wants fresh, efficient pizza, a combi is the way to go.

Remember: Just like choosing toppings, there’s no right or wrong answer. Similarly, it’s all about finding the boiler that fits your needs and tastes!

Pros and Cons of System Boilers

This is a good breakdown of the pros and cons of system boilers.


  • Hot water party: Imagine a pool of hot water always ready to fill your bathtub in seconds. That’s a system boiler!
  • Multitasking master: Need hot water in the kitchen and the shower at the same time? No problem for this champ!
  • Speedy delivery: Forget waiting for water to heat up. This boiler has a built-in pump that delivers it like a lightning bolt.
  • Sun-powered friend: You can team it up with solar panels for eco-friendly hot water, like a superhero with a solar suit!
  • Electric backup: In a pinch, you can plug in an electric heater for extra hot water power.


  • Big tank, big thirst: If you use all the hot water, you’ll have to wait for it to refill, like a thirsty dragon waiting for a new lake.
  • Planning ahead: Need hot water at 5 AM? Set the timer the night before, or you might end up with a cold shower surprise!
  • Space hog: This champion needs its own corner, so make sure your home has enough room for its tanky glory.
  • Temperature drop: The hot water gets a little cooler as it travels, like a pizza getting lukewarm on the way home. Good insulation helps keep it warm!
  • More to fix, more to pay: With more parts, there’s a higher chance of something going wrong, which means more repair costs. Think of it like a superhero with lots of gadgets – more gadgets, more maintenance.
  • Low pressure panic: If your water pressure is weak or your radiators are old, this powerful boiler might not be the best fit.

Is the Combi King or Knave? Unmasking the Hot Water Hero for Your Home

Forget dragons guarding fiery waterfalls – the real battle for hot water dominance lies within your home! In the red corner, we have the challenger, the Combi Boiler. Without reservation, this compact champion promises instant splashes of steaming glory, but can it truly conquer your hot water needs?

Don’t be fooled by its size, though. Undeniably, this modern marvel boasts impressive efficiency and space-saving tricks, making it a popular choice for smaller kingdoms. However, its reign is destined to be short-lived, or can it rise above the limitations and claim the throne of your hot water kingdom?

Before we crown the champion, let’s delve into the Combi’s strengths and weaknesses.


  • Efficiency Champ: Think of a combi as a superhero who uses less energy and saves you money on your bills, like a recycling superhero who turns trash into treasure!
  • Instant Hot Water: No more waiting for pre-heated water! Combi heats it up on demand, like a lightning-fast chef whipping up a hot meal.
  • Space Saver: No bulky hot water tank needed! Combi is like a tiny superhero who lives in a compact apartment, perfect for small homes.
  • High-Pressure Hero: Imagine a powerful shower spray like a superhero washing away all the grime! Combi delivers high-pressure water, depending on your home’s usage. 


  • Hot Water Hog: If everyone uses hot water at once, Combi might struggle to keep up, like a superhero overwhelmed by villains. Not ideal for big families or multiple bathrooms.
  • Patience Power: Unlike a system boiler’s instant delivery, Combi needs a few seconds to heat up the water, like a superhero needing to charge their powers before unleashing them.
  • Pressure Panic: Low water pressure can weaken Combi’s superpower, like a superhero losing their strength in a kryptonite chamber. Check your home’s pressure before choosing.
  • Pipe Power Up: Older plumbing might not be strong enough for Combi’s high-pressure water, like a superhero needing to upgrade their suit before taking on tougher challenges. Consider pipe replacements if needed.

System Boiler vs Combi Boiler Running Cost

Combi and system boilers vary in costs, considering brand, model, and installation complexity. For example, natural gas boilers might need an extra gas line, and electric combi boilers could require a special electrical circuit, driving up costs. Moving a system boiler is pricier due to the water cylinder, resulting in higher labor charges and additional materials.

Typically, combi boilers cost between £500 and £3,000 upfront, with installation ranging from £300 to £500. System boilers run £1,800 to £2,800 upfront, with similar installation costs. Overall, budget around £900 to £3,500 for a combi and £2,100 to £3,300 for a system. 

Despite these costs, a solution exists. The UK government provides boiler grants, making it more affordable for everyone to get a new boiler. This financial assistance significantly reduces overall expenses.

Combi vs System Boiler. Which One is the Best?

Declaring one boiler “better” than the other wouldn’t be fair, like announcing a winner in a pie-eating contest without considering everyone’s preferences. Both combi and system boilers have their own strengths and weaknesses, making them ideal for different situations. Here’s a quick recap:

Combi Boiler

  • Pros: Compact, efficient, instant hot water, good for smaller homes and low energy bills.
  • Cons: Might struggle with high hot water demand, not ideal for multiple bathrooms, needs high water pressure.

System Boiler

  • Pros: Consistent hot water flow, handles high demand well, good for larger homes and multiple bathrooms.
  • Cons: Takes up space, needs a hot water tank, less efficient, can run out of hot water if not planned.

Here are some additional factors to consider:

  • Number of bathrooms: A combi might struggle with multiple bathrooms simultaneously.
  • Hot water usage: Do you take long showers or use hot water for laundry often? A system might be better.
  • Space: Do you have room for a hot water tank?
  •  Water pressure: Low pressure might not be enough for a combi.

Ultimately, the best way to choose is to consult a qualified plumber or heating professional. They can assess your specific needs and recommend the boiler that’s the perfect fit for your hot water kingdom!

Remember, there’s no shame in asking for help. Choosing the right boiler is a big decision, and a trusted expert can guide you through the plumbing maze and ensure you get the hot water happily ever after you deserve!


In the showdown of Combi vs. System boilers, pinning down a champion is a tricky task. It’s like choosing between flavors of ice cream—everyone has their favorite. 

Combi brings the zing of on-the-spot hot water, perfect for quick showers. On the other hand, System exudes reliability, an ideal fit for larger households.


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