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Combi Boilers

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Combi Boilers

Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: April 13, 2021. Updated: May 16, 2024

Are you considering a heating upgrade for your home and wondering if changing to a combi boiler is the right fit? Or do you already have a combi boiler and need a replacement new boiler? You’ve come to the right place.

A combi boiler is a highly efficient, space-saving solution for both heating and hot water. They are particularly good for small to medium-sized flats and homes. Below, we’ll review how these all-in-one units work, their advantages, and how to choose the best combi boiler for your needs without the jargon.

Key Takeaways

  • Combi boilers are space-saving, dual-function units that provide both home heating and immediate hot water, eliminating the need for separate water tanks or cylinders.
  • Energy efficiency is one of the main advantages of a combi boiler. Some models, like the Viessmann Vitodens 200-W gas combi boilers, achieve efficiency levels of up to 98%, leading to reduced carbon footprint and energy bills.
  • Correct boiler installation and regular maintenance by Gas Safe registered engineers are vital for the safety, optimal operation, and longevity of combi boilers. Annual checks and system maintenance are recommended.

Understanding Combi Boilers

The concept of a combi boiler is straightforward. Combination boilers (aka combi boilers) are a great solution for home central heating and hot water. They seamlessly merge both functions into one compact unit. This means no bulky water storage cylinders or tanks. They’re compact and space-efficient, which simplifies installation and annual servicing.

These adaptable boilers ensure warmth and comfort in any living space, from cosy apartments to modest-sized houses, without taking up too much room. Combi boiler pipes can look daunting, but our guide will help you fully understand each of them.

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How a Combi Boiler Works

If you’re wondering how does a combi boiler work, you’re not alone. An oil, LPG, electric or gas combi boiler heats water in the pressurised central heating system through the primary heat exchanger. This hot water is then pumped around the central heating pipework and radiators.

When a hot water tap or shower is turned on, the hot water heated in the primary heat exchanger is diverted (using a diverter value) to the secondary plate heat exchanger. This is where the hot water inside your central heating transfers heat to incoming, fresh water.

When you turn on a hot tap or your central heating system kicks on, the boiler turns on and heats water almost instantly, with the only delay being the distance from the boiler to the tap or shower.

With no stored hot water to worry about, you say goodbye to the relatively low efficiency of keeping a tankful of water hot and the frustration of running out.

Combi boiler cross-section - Boilerhut

Combi Boilers save space

As combi boilers are a single unit and don’t requite central heating water tanks or cylinders they can often free up space in cupboard and lofts. For example, back boiler replacement or changing from a conventional boiler will allow the removal of both the cold water storage tank and the hot water cylinder.

These compact units are designed to fit snugly within a kitchen cupboard or utility room, making them the ideal heating solution for properties where space is at a premium. As a hot water and central heating solution, a gas combi boiler is both efficient and space-saving. The smaller the flat or home, the bigger the potential return of space becomes.

Energy Efficiency and Cost Savings

A great combi boiler is highly efficient. Thanks to condensing technology, new boilers make the most out of every unit of energy, achieving staggering efficiency levels of up to 98%. The Viessmann Vitodens 200-W and 111-W storage combi boiler are perfect examples.

Stainless steel heat exchangers are another way to ensure lifelong efficiency from a boiler. Aluminium can lose up to 10% efficiency over 10 years, costing the owner more money over time. Stainless steel remains efficient for over 15 years.

Combi boilers, which heat only the water you use, are economical and environmentally friendly, helping to decrease your carbon footprint and energy bills.

This efficiency doesn’t just benefit you in the short term; it supports an environmentally sustainable future, making combi boilers a responsible choice for eco-conscious homeowners.

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Selecting the Perfect Combi Boiler for Your Home

Several factors, including the size of your property, the number of bedrooms, and your typical hot water usage, influence the best combi boiler for you. It’s also important to consider the potential simultaneous demands on your system. For example whether you’ll need to run multiple showers or hot water taps at the same time.

A modern combi boiler, with their innovative pre-heat systems, are designed to respond swiftly to these demands, ensuring that you have hot water when and where you need it. Adding to the mix are considerations of water pressure, the layout of hot water outlets, and the overall flexibility of installation, all of which play a role in determining the perfect combi boiler for your unique living situation.

Viessmann’s High-Efficiency Gas Combi Boilers

Viessmann is a leader in high-efficiency combi boilers. Their gas combi boilers, like the acclaimed Vitodens 100-W combi, are renowned for their performance, reliability and 12-year warranty. The 111-W model, with its integrated hot water cylinder, is designed to handle high hot water demands. Both testaments to Viessmann’s commitment to quality and performance.

Viessmann’s 200-W model is one of the most efficient boilers in the world at 98% efficient. The 200-W is perfect for homes that require super-efficient central heating.

Worcester Bosch Combi Boilers

Worcester Bosch is a well-known brand in the UK for their reliable and trusted heating and hot water solutions. The Greenstar combi boiler range caters to almost every home specification. With various power outputs and warranty periods available, you can find the perfect fit for your home.

Alpha combi boiler range

Alpha boilers are part of an Italian, family-owned business called Immergas. They are relatively new in the UK, but all of their boilers have stainless steel heat exchangers. This ensures ongoing efficiency.

Navien Oil combi boiler range

An oil combi boiler offers an efficient heating and hot water solution for homes without access to the mains gas grid. Navien Blue Flame technology ensures their oil boilers deliver robust heating and ample hot water across various property sizes. These boilers from Navien are highly efficient and use a stainless steel heat exchanger to ensure lifelong efficiency.

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Installation and Maintenance of Your New Boiler

The path to a cosy and comfortable home extends beyond choosing the right combi boiler. Correct installation and maintenance are crucial for optimal boiler operation and safety. In the UK, only Gas Safe registered engineers are authorised to install and service gas and LPG boilers. Engineers should be registered with APHC or OFTEC for oil boiler installations.

Partnering with a reputable boiler supplier like Boilerhut means you’ll get top-quality products and the assurance of exceptional installation services by professionals who know their craft inside and out.

The Importance of Professional Installation

Though combi boilers have a streamlined design that simplifies installation, a professional install and setup remains indispensable. Gas Safe Registered Engineers have the qualifications and legal authority to ensure your combi boiler is installed with precision and care.

This isn’t just about following protocols; it’s about safeguarding your investment and the well-being of your household. An expertly installed boiler is the foundation of a reliable heating and hot water supply for years.

Keeping Your Combi Boiler in Top Condition

Routine combi boiler servicing by a Gas Safe registered engineer is not just recommended but necessary to maintain your warranty and keep your boiler in optimal condition. But it’s not all about safety; regular maintenance also means efficiency. By identifying potential issues early, you can prevent costly breakdowns and keep your heating bills in check.

Also, don’t overlook the benefits of periodic system flushing, short summer boiler runs, and checking your radiator valves; these simple measures can go a long way in preventing blockages and ensuring your boiler responds efficiently when the chill of winter sets in.

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Comparing Combi Boilers to Other Boiler Types

The types of boilers available are:

Whilst a combi boiler may not be the best fit for every situation, they are a popular choice for small and medium-sized homes and flats.

Larger homes with multiple bathrooms might find a system boiler, with its separate hot water cylinder, better suited to their high water demands. Conventional boilers are best for homes with poor cold water pressure as they have a header tank to provide a constant feed of cold water.

It’s worth noting that system boilers and conventional boiler setups are prone to running out of hot water if there has been a high demand.

If you are considering a switch from a conventional to a combi system, be prepared for a large overhaul, as this change often requires additional pipework.

Why Homeowners Choose Combi Boilers

The increasing popularity of combi boilers among homeowners is due to their compact size, energy efficiency, and the ability to provide hot water immediately. These convenient units provide a level of independence in heating and hot water functions that is particularly attractive when both are needed at once. The immediate response to heating demands means never having to endure a cold shower or a chilly room.

Navigating the Range of Combi Boilers in Stock

Numerous leading boiler brands offer a vast array of oil and gas combi boilers, each equipped with unique features and benefits to meet varying needs. Whether you’re looking for something basic or a unit packed with the latest technology, brands like Worcester Bosch and Viessmann have you covered with award-winning selections of various sizes and outputs.

In particular, Viessmann’s Vitodents range, with its stainless steel heat exchangers and integrated WiFi for fault monitoring, continues to top ‘best boiler’ lists, a testament to the brand’s commitment to quality and innovation.

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Save up to £590 PER YEAR on your heating bills.
Quote in 30 seconds. No obligation. Next Day installation.
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These compact and efficient units are more than just a central heating system; they’re a smart investment in your home’s future. Plus, you can save up to £590 a year on your heating bill with modern combi boilers.

Their space-saving design, energy efficiency, and the convenience of instant hot water make combi boilers an attractive option for homeowners. With the knowledge to choose the right model, ensure proper installation, and perform regular maintenance, you are well-equipped to enjoy the warmth and comfort of a well-heated home while reaping the benefits of lower energy bills and a reduced environmental impact.

Need a new boiler?

If you need a new or replacement boiler or are looking at having a central heating system installed, get an online quote (it takes less than 1 minute), and you’ll get an instant price. But why choose Boilerhut:

Our Top Selling Combi Boilers

Viessmann Vitodens 050 W - Viessmann boilers reviews | Boilerhut

Viessmann Vitodens 050-W Combi Boiler

  • Size: 25kW to 35kW
  • Efficiency: 94%
  • Warranty: 10 Years

Worcester Greenstar 8000 Style Combi Boiler

  • Size: 30kW to 50kW
  • Efficiency: 94%
  • Warranty: 12 Years
Viessmann Vitodens 100-W - Heat Pump vs Gas Boiler | Boilerhut

Viessmann Vitodens 100-W Combi Boiler

  • Size: 11kW to 32kW
  • Efficiency: 94%
  • Warranty: 12 Years
Viessmann Vitodens 200-W - Types of boiler | Boilerhut

Viessmann Vitodens 200-W Combi Boiler

  • Size: 30kW, 35kW
  • Efficiency: 98%
  • Warranty: 10 Years

Ariston Clas ONE Combi Boiler

  • Size: 24 kW, 30 kW, 38 kW
  • Efficiency: 90%
  • Warranty: 8 Years
Alpha E-Tec Plus NX - Alpha Boilers Reviews | Boilerhut

Alpha E-Tec Plus NX Combi Boiler

  • Size: 28kW to 38kW
  • Efficiency: 93%
  • Warranty: 10 Years
Viessmann Vitodens 111-W | Boilerhut

Viessmann Vitodens 111-W Storage Combi Boiler

  • Size: 25kW & 32kW
  • Efficiency: 98%
  • Warranty: 10 Years
Worcester Bosch Greenstar Heatslave II - Oil Combi Boilers | Boilerhut

Worcester Bosch Greenstar Heatslave II Oil Combi Boiler

  • Size: 18kW, 25kW or 32 kW
  • Efficiency: 94%
  • Warranty: 10 Years
Navien LCB700 Regular Boiler | Boilerhut

Navien LCB700 Blue Flame Oil Boiler

  • Size: 21 kW, 28 kW, 36 kW
  • Efficiency: 93%
  • Warranty: 7 Years

Frequently asked questions

You need to consider your property’s size, number of bedrooms, and hot water usage to determine the right size for your combi boiler. These factors will help you find the most suitable option for your home. Use our boiler size calculator to learn more.

The main advantages of combi boilers compared to other types are space-saving design, energy efficiency, and the convenience of providing hot water on demand without the need for storage tanks. These factors make combi boilers a practical choice for many households.

The downside of a combi boiler is its reliance on good mains water pressure and its inability to provide high volumes of hot water through multiple outlets. These limitations should be considered before making a decision.

Yes, combi boilers are environmentally friendly due to their high energy efficiency and reduced CO2 emissions.

Whether your combi boiler runs on mains gas, oil or LPG, the fuel enters a sealed combustion chamber inside the boiler and an electric ignition sets it alight.

The primary heat exchanger within the boiler then heats incoming water up to the required temperature, which then flows through all of the radiators in your home or is delivered to taps and showers, as needed.

Combi boilers have two heat exchangers inside them:

  1. A primary heat exchanger (for central heating and hot water)
  2. A secondary plate heat exchanger (for hot water)

The primary heat exchanger heats and recycles the water that goes through the pipes into the radiators.

The secondary plate heat exchanger uses that returning hot water from radiators, and heats up sealed pipes with potable water that goes into your taps.

Our guide will provide more detail about how combi boilers work – How Does a Combi Boiler Work?

If you are planning to install your new combi boiler in the garage and you have a bathroom on the other side of the house, you could experience a delay in the time it takes for water to heat up and reach your taps and showers. For best results, your combi boiler should either be installed reasonably close to your bathroom, or equidistant to the kitchen taps and bathroom.

Yes. In general, boilers can be installed anywhere in a property. Owners like lofts as they are out of the way and don’t take up kitchen, utility or airing cupboard space. However, it’s worth remembering that if the boiler needs resetting or the pressure drops and needs filling up you may need to get to that combi boiler in the loft. This may not be the easiest thing to do for everyone.

Read more in our boiler in the loft guide >

Yes. But there are considerations; how far is it from bathrooms and taps, is it insulated, etc. Read our post on garage installations here >

Yes. In general, boilers can be installed anywhere in a property. It all depends on the pipework and where the gas supply enters the property. If you have room in your bathroom for a boiler there is no reason you can’t install it in there.

It’s a widespread assumption that gas boilers operate without electricity, relying solely on the gas supply. However, this isn’t the case. Despite gas being the main fuel, gas boilers do require a small amount of electricity to function.

Read our guide on electricity usage >

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