Jun. 16, 2025
Buying a new boiler is a massive investment for any homeowner, but it can also be a pretty tricky process.
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Get it right, and you can have peace of mind for many years to come, enjoying all the benefits that come with a high-performance, energy efficient boiler.
But get it wrong, and you’re in for a world of trouble, not to mention even more expenses down the road.
The $64,000 question is:
How do I know which boiler to buy?
At Plumbing Superstore, our customers often ask us exactly this. That’s why we decided to put together the ultimate boiler guide that will provide plenty of help with buying a new boiler.
Here’s what we’re going to cover.
Before we dive into the various types of central heating boilers available on the UK market, we need to get a basic understanding of how boilers actually work.
Here’s the deal:
Your boiler works by burning a fuel source, such as natural gas, Liquefied Petroleum Gas (LPG) or electricity, in a combustion chamber to produce heat. This heat is then transferred to water or another fluid within the boiler through a heat exchanger.
As the water absorbs the heat, it undergoes a phase change, turning into steam if high temperatures and pressures are reached or simply becoming hot water in lower-pressure systems.
Now:
The steam or hot water generated in the boiler is then used for various purposes, such as heating buildings, producing electricity in power plants or driving industrial processes. To ensure safe operation, boilers are equipped with safety mechanisms, including pressure relief valves and temperature controls. In addition, they may employ advanced features like condensation to maximise energy efficiency.
All in all, boilers play a crucial role in providing heat and power for a wide range of applications, making them essential components in many industries and residential heating systems.
If you want to find out more about how central heating works in general, check out our guide.
Gas central heating wet systems are currently the prevailing choice in the UK, although electric wet central heating systems are occasionally encountered. As most boiler guides will tell you, gas boilers are the preferred option for several reasons.
Here’s the scoop:
Firstly, the majority of UK residences are already connected to the gas network, offering a convenient heating solution.
Secondly, gas is more cost-effective than many alternative heating sources, resulting in savings on energy bills.
Thirdly, the UK has substantial gas reserves in the North Sea, ensuring a reliable domestic supply without the need for extensive gas imports.
Having said that, we should point out that fossil fuel boilers (gas, oil and LPG boilers) are set to be phased out after in line with the UK Government’s renewed commitment to achieving Net Zero by – although some exemptions will be in place to help households transition to renewable energy sources.
With that in mind, let’s delve into the different boiler types:
Combi (combination) boilers efficiently provide both heating and hot water on demand from a single unit. Their compact size and straightforward maintenance make them popular, especially in smaller homes and flats where space is limited. Combi boilers are cost-effective, provide an immediate supply of hot water and are favoured in new builds.
Conventional boilers, also known as regular or heat-only boilers, operate in an open-vented system with external components like pumps and valves. They excel at heating rooms for extended periods but do not supply hot water, limiting their versatility.
Conventional boilers are simple in design and cost-effective. They work well with older radiators and are suitable for budget-conscious consumers.
System boilers combine features of both conventional and combi boilers.
Check this out:
They have a substantial hot water cylinder but run in a sealed system. Ideal for larger homes with multiple bathrooms and high hot water demand, system boilers ensure consistent hot water flow to multiple outlets simultaneously. However, they are larger in size due to the hot water storage cylinder.
In case you’re wondering:
No, hot water doesn’t need to be continuously on for central heating, as properly insulated cylinders can maintain heat for hours or even a day after being heated by the boiler or immersion heater.
If you’ve been thinking about getting a new boiler for a while, you’ve probably come across the terms ‘condensing’ and ‘non-condensing’.
But how do they differ? Let’s find out!
Condensing and non-condensing boilers differ primarily in how they handle the combustion process and utilise the heat produced. In effect, a condensing boiler is a far better energy-saving boiler, designed to maximise energy efficiency by extracting additional heat from the exhaust gases that would otherwise be lost.
The thing is:
In a condensing boiler, the combustion gases cool down to the point where water vapour in the exhaust condenses into liquid water. This phase change releases latent heat, which is captured and used to preheat the incoming cold water. The process significantly increases the boiler’s efficiency, often reaching mind-blowing efficiency levels of up to 99%.
What’s more:
Condensing boilers are typically more environmentally friendly and cost-effective in the long run because they consume less fuel and produce lower emissions. They are particularly suitable for modern heating systems, including underfloor heating, where lower water temperatures are used.
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Non-condensing boilers, on the other hand, can’t capture this latent heat from the exhaust gases. So, they release the hot gases into the atmosphere, resulting in lower energy efficiency, typically around 70-80%. As a result, these boilers are often found in older heating systems that run at higher water temperatures, such as traditional radiator systems.
However, it is now illegal to install non-condensing boilers in the UK, as government regulations state that new boilers must have a minimum efficiency of at least 92%.
At the end of the day, the best boiler type will vary depending on the size of your home and household and your specific needs. Combi boilers are many buyers’ go-to choice because they’re compact and easy to maintain. With a larger house, though, you might want to consider a system boiler.
In any event, when choosing a boiler, you should consider the following factors:
Keep in mind that different boiler types tend to have different lifespans.
Now that we’ve covered the various types of boilers, we need to discuss boiler sizes.
Boiler size or output is measured in kilowatts (kW). And, once you’ve made up your mind about the type of boiler you intend to buy, you’ll need to figure out what size you require.
In general, that will depend on the size of your home. Specifically, the key elements in the equation are:
Keep in mind that the state of your insulation will also play a huge role. If you live in an older, poorly insulated property, you’ll need a boiler with a considerably larger output to maintain a similar temperature to the one you would in a new build with state-of-the-art insulation.
With that caveat in mind, here’s a breakdown of the most common scenarios for combi and system boilers.
Combi boilers have to be more powerful than the alternatives because they have to heat the home while simultaneously producing hot water on demand.
BedroomsBathroomsRadiatorsRecommended boiler size 1-21Up to -27kW 2---34kW 4+3+15--43kWIf you’re wondering why system boilers in particular have to be less powerful than combi boilers, there’s a simple answer:
System boilers have a separate hot water cylinder that takes care of your domestic hot water (DHW) needs.
BedroomsBathroomsRadiatorsRecommended boiler size 1-21Up to 109-18kW 2---26W 4+3+15--40kWWith so many different boiler types and sizes currently available on the UK market, by this point you’re probably wondering how much buying a boiler is going to set you back, right?
That’s exactly what our boiler recommendations are going to zoom in on next.
As we’ve already mentioned on a couple of occasions in our boiler guide, buying a new boiler can be a very expensive proposition.
Just how expensive will ultimately depend on several factors, including:
Given the number of variables in question, it’s virtually impossible to calculate exactly how much your boiler replacement is going to cost.
No need to despair, though! Here are some estimates of your likely boiler replacement costs:
A new boiler by itself is likely to set you back anywhere between £500 and £3,000 plus VAT.
But that’s not all:
Your new boiler must be installed by a certified specialist. So, you’re looking at another £1,500 plus VAT in installation costs on average, once again depending on your boiler options.
In general, a like-for-like swap will be cheaper, unless you need to change the location.
Buying a new boiler can be quite challenging. We hope our boiler guide for buyers has given you a head start so that you know what factors to bear in mind.
The bottom line is:
Consider your budget, including installation costs and long-term operational expenses, to find a boiler that balances your needs and financial constraints.
Consulting with a qualified heating professional for up-to-date boiler advice can help you make an informed decision tailored to your specific circumstances.
Condensing boilers are some of the most efficient available, creating the most heat energy possible from your fuel source and reducing costs. Replacing your old boiler with a condensing boiler has been found to save homeowners hundreds of pounds per year. For many customers, though, the question remains of exactly what is a condensing boiler? Condensing boilers function in largely the same way as your existing boiler, burning fuels such as oil or natural gas, but they differ in the way they make use of the resulting heat energy. These boilers have a number of benefits but they aren't an ideal fit for every home and every customer, so it's important to take some time to examine the positives and negatives before buying.
On the whole, condensing boilers function in a similar method to traditional boilers. A burner is supplied with fuel, producing a flame, which then warms fluid in your central heating system as it passes through a heat exchanger. In traditional, non-condensing boilers, this process produces a significant amount of water vapour that is vented away from the system, resulting in wasted heat energy. Condensing boilers increase their efficiency by taking this steam, produced when the hydrogen content of fuel is burned, and condensing it into liquid form, putting the residual heat to good use. As a result, less heat energy is required from your burner and the boiler's fuel demands are reduced. This can typically improve boiler efficiency by as much as 12%. How effective this process is depends on the temperature of the water vapour but in the majority of cases it will result in more efficient heating.
It's essential to find a suitable boiler for the size of your home and the number of radiators contained within. While condensing boilers are almost always more efficient than an equivalent traditional unit, this saving will be cancelled out if you purchase an unnecessarily large boiler for your property. For this reason, it's best to install the smallest possible condensing boiler that will comfortably supply your central heating system (and hot water, if applicable). Some modern condensing boilers are fitted with a control panel that initially activates the boiler in condensing mode but later reverts to standard functions, making them lose efficiency over time. This initial condensing period should still result in more efficient heating overall, generally making condensing boilers the better choice.
It's also important to ensure your heating system and boiler are installed properly; incorrect settings can result in a lack of condensation in the boiler, losing the major benefits of a condensing unit. The lower the temperature of water when it enters the boiler, the more likely it is to cause condensation when heated. Ideally, returning water should be less than 55°C by the time it enters the unit. As a result, even older, lower temperature heating units such as cast iron radiators can be a great match for a new condensing boiler.
In the early years of condensing boilers, it was commonly believed that they were less reliable than conventional models. One of the most noticeable issues early on was that of “pluming”, a visible white plume of condensation from the outlet flue. Although this was unrelated to any sort of mechanical fault, a common perception was that this was the result of a problem with the boiler. Lack of familiarity for engineers and plumbers was also an issue in the early years, as condensing boilers have a number of unique features. This led to instances where mechanical failures would occur because of incorrect installation, rather than boiler faults. As a result, they have carried this reputation into the present day, unfairly for the most part.
At the same time, there are some genuine issues with condensing boilers. The most significant of these is that the liquid produced in the condensing process is slightly acidic (between pH3 and pH4), which can increase the rate of corrosion in the boiler's heat exchanger. This is also a result of older boilers using thicker exchangers, which were slower to heat but more resistant. While this vapour can be corrosive, it poses no danger to people or pets. As a result of this acidity, condensing boilers only utilise certain materials in their manufacturing: steel and aluminium are commonly used, whereas traditionally common materials such as copper and cast iron are not suitable. It can be beneficial to monitor your heat transfer fluid; anti-corrosion agents can be used to maintain a slightly alkaline fluid between pH8 and pH9. It is believed that this will reduce the rate of corrosion. It is difficult to predict the lifespan of a condensing boiler with certainty, given how recent the technology is. However, most manufacturers offer a warranty of around five years on condensing boilers and sometimes longer on the heat exchanger unit, particularly if they're made of stainless steel.
Since their introduction, several countries have made their use compulsory or offered financial incentives for installing them. In the UK, it has been compulsory since that all new gas boiler installations must be modern, high-efficiency condensing boilers. While there is more leeway with new oil boilers (particularly warm air central heating systems) the use of condensing boilers is still encouraged and their rapid spread around the world has shown no signs of slowing down.
Condensing boilers are currently more expensive than conventional boilers, often costing as much as 50% more than their older counterparts. However, the Building Research Establishment (BRE) have claimed that this increased cost should be negated in between two and five years of installation thanks to reduced fuel use. How significant the difference in your fuel usage is will vary depending on how often your new boiler is used, the age and efficiency of your original unit and the difficulty of installing your replacement. As governments embrace the environmental benefits of condensing technology and manufacturers abandon conventional boilers, costs are gradually being reduced.
Servicing should be no more expensive and time consuming than with traditional boilers. The Building Research Establishment has conducted extensive research into condensing boilers and found that, on the whole, they do not require servicing any more often than traditional boilers and are just as reliable. The only additional task is to ensure the condensate drain is functioning properly. The BRE also stated in their findings that condensing boilers were, at the very least, consistently more efficient and had reduced fuel demands in comparison to their traditional counterparts.
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