Shopping for a new boiler can be frustrating, particularly when it seems like prices can vary massively from one manufacturer to another. And then there’s the costs with installation, without installation, with smart thermostats, without smart thermostats. If you’re looking for a simple guide to boiler costs, then you’re in the right place.

We’ve designed this guide to help you to understand the basic costs involved in purchasing different types of gas boilers. We’ll walk you through all the important areas that impact your choices when looking for a new boiler, including maintenance and operating costs and not just the initial outlay.

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Considerations when buying a new boiler

When buying a new Viessmann boiler, you might be tempted to cut corners and save some money. This is false economy. Always use a Gas Safe registered installer for any boiler replacement work, this will ensure your warranty is valid. If you have the option of a longer warranty period, please note that many warranties require an annual service to remain valid.

Carefully consider which brand you purchase as performance and reliability can vary dramatically by brand. While it may seem logical to buy a budget brand and hedge your bets, it could affect you negatively. New boiler costs for budget ranges often reflect the shorter warranty period and lack legacy support for spare parts.

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New boiler costs

Combi boilers - £700 to £3,500

Combi boilers have quickly become one of the most popular forms of gas boilers. This is because they don’t just provide hot water to your central heating system, but can heat water on demand, meaning you can do away with a large cylinder. This is ideal for homes that may not have a lot of space for storage tanks. There are however limitations to how much hot water a combi can deliver so they are generally not recommended for larger properties with more than one bathroom.

If you’re replacing like for like, i.e. a combi boiler for another combi boiler, then fitting costs will be reduced compared to if you were switching a combi for another type of boiler, like a conventional boiler. We discuss installation costs a little further down the guide.

For now, let’s take a look at the available options using a mid-ranged combination boiler as a reference.

  • What is the cost of a combi boiler?

Below, you can find the average cost of a mid-range combi boiler (excluding installation). The price will vary depending on which boiler you go for and the manufacturer. 

Size of your property

Estimated new combi boiler cost

Small house or flat (up to 3 bedrooms)

£700 to £1,500

Semi-detached or terraced (up to 4 bedrooms)

£800 - £2,000

Detached home (3 bedrooms or more)

£1,000 - £3,500

These costs could also increase if you want an extended warranty (most manufacturers offer a warranty of up to five years as standard, but it could cost more if you wanted to have this for 10 years, for example).

Conventional boiler costs - £700 to £2,500

A conventional boiler doesn’t heat water on demand like a combi boiler does. Instead, the water is heated according to the programme and stored in a hot water cylinder until it’s needed. You’ll know if you have this kind of system as you will likely have an airing cupboard or a water cylinder elsewhere in the house.


Conventional boilers were the main choice of system up until around 10 years ago, when combi and system boilers became the more popular option.

Size of your property

Estimated boiler installation cost

Small house or flat (up to 3 bedrooms)

£700 to £1,400

Semi-detached or terraced (up to 4 bedrooms)

£800 to £1,700

Detached home (3 bedrooms or more)

£1,000 to £2,500

If you already have one fitted and you’re swapping like for like, a new conventional boiler should cost anywhere between £700 and £2,500, depending on the size or manufacturer you go for. This is the cost just for the boiler. If you wished to have other aspects of the system replaced, including the hot water cylinder, cold water storage tank, pipes or radiators, then the cost would go up.

System boiler costs - £700 to £2,500

A system boiler works in the same way as a conventional boiler, the difference being a system boiler incorporates a pump and a sealed system kit, meaning there is no requirement for an external pump or feed and expansion tank on the heating circuit.. They work much like a regular boiler in that they heat the water according to a programme and store it in a cylinder, this can be a vented or unvented cylinder. This means they’re better for homes that don’t have a loft or that have limited loft space or access.

These systems are popular because they mean you get to keep your hot water tank/airing cupboard. Generally, systems that store water like this in a tank also have higher pressure than combi systems that deliver the hot water on demand. Because the boiler unit is a single unit, you don’t need to pay for a cold water tank in your loft.

Size of your property

Estimated system boiler cost

Small house or flat (up to 3 bedrooms)

£700 to £1,200

Semi-detached or terraced (up to 4 bedrooms)

£800 to £1,700

Detached home (3 bedrooms or more)

£1,000 to £2,500

If your home doesn’t already have a hot water tank, then you may also need to pay extra to have one of these purchased and installed.

Installation costs

The costs we’ve covered above are the basic costs for the boiler unit itself, but installation is when costs can begin to vary widely. This is because installation can be based on all sorts of things, including the current system in your home, what you require, how much work is involved, which engineer you go for and even where you live (London prices tend to be much higher than elsewhere).

Unfortunately, unlike some appliances, a boiler isn’t one that you can install yourself and so you will need to rely on a Gas Safe-registered engineer to do this for you, and therefore these costs do need to be considered.

When you’re gathering quotes and trying to decide on an installer, it’s good to have an idea of installation price in your head, which you can find below.

How much does it cost to install a combi boiler?

On top of the cost of the boiler itself, you could expect to pay £600 for a basic swap (combi for combi). If you want the combi to be moved to another location, you could pay around £1,100. 

How much does it cost to install a conventional or system boiler?

Conventional boilers could be a little more expensive to replace. If you’re swapping a conventional boiler for another of the same, installation could cost £900. For a conventional boiler that’s being moved to another location, installation could go up to £1,200.

When it comes to system boilers, you could look to pay £950 for a like-for-like swap. If the system boiler is being installed in a different location, these prices should be similar to combi prices.

Installation scenarios

In our above examples, we’ve mentioned swapping each boiler like for like, or moving it to another location. But there are so many more installation scenarios that can affect cost and so we thought we’d list some of them here for you.

  • Replacing a conventional boiler with a combi system

When you’re replacing a conventional boiler with a combi system, you’ll likely pay extra as the hot water cylinder will need to be drained, disconnected and removed. This could cost around £1,500 in installation fees.

  • Replacing a combi boiler with a conventional one

If your home has a combi boiler but you want a conventional system, then a hot water cylinder will need to be reinstalled, bringing installation costs to around £1,700.

  • Back boiler removal

Back boilers are a thing of the past thanks to UK regulations, so you can’t replace a back boiler with another back boiler. However, you may wish to replace it with a conventional system instead, which could cost around £2,500. This includes the back boiler removal and installation of the new regular boiler, hot water tank and cold water feed.

For all of the above, the prices could increase even more if you’re converting the system and moving the boiler too. Moving a boiler generally increases the installation fee by £300 to £500.


Additional costs to look out for

Ok, we’ve covered the costs of a new boiler as well as installation fees. But before we wrap up, there are some extra costs to consider as well.

  • Replacing gas pipes - £300

Sometimes, it’s not possible to use existing gas pipes, and this is usually because they don’t meet regulations. The pipe standards used to require a pipe width of 15mm, but this has since been upgraded to 22mm. They may need to be replaced and this will be dependent on the boiler type and length of pipe.

  • Power flush - £500

Over time, our heating systems can build up a lot of rust and sludge that can affect the efficiency of the system and also cause cold spots in radiators. A power flush involves pushing water through the system at high pressure to dislodge and flush out a lot of this debris. It can be worthwhile, but it could set you back another £500.

  • New smart thermostat system - £200

You may wish to upgrade your heating system so that you have greater control. This can be done with a smart thermostat, which allows you to change the set temperature on your phone (even when you’re not home) and to zone your house so different rooms can be set to different temperatures. These can increase the efficiency of your system, so the initial cost becomes more of an investment.

  • Chemical flush - £200

A chemical flush is slightly different to a power flush, in that it doesn’t use high-pressure water but chemicals to remove sludge and dirt. It’s another effective way of cleaning out your heating system.

  • New radiators

If your radiators are quite old, they may not be as efficient as they once were and could even decrease the efficiency of your boiler, too. They can cost around £100 per radiator.

  • Flue movement - £500

When a boiler is being relocated, it is often the case that the flue needs to be moved too. You could expect to pay an additional £500 when a flue is moved from a horizontal position to a vertical position (so it exits via the roof instead of from a wall).

  • Extended warranties - £150

Most boilers, including Viessmann’s, will come with a warranty, but some people choose to extend this so they know their boiler is covered for longer should anything go wrong. If you wish to extend the warranty from, say, five to 12 years, you could expect to pay up to £150, this could be more if the boiler is bigger or has more features.


Considerations when buying a new boiler

When you’re buying a new boiler, it can be tempting to cut corners. You may think you don’t need your pipework updating or your old, unused cylinder taking out. However, we’d strongly advise that it’s worth paying for these things.

For any gas boiler work, you should use a Gas Safe-registered engineer and ensure that you keep on top of the boiler’s annual service, as both of these things will ensure that your warranty remains valid.

Carefully consider which brand you purchase from, as performance and reliability can vary dramatically by brand. While it may seem logical to buy a budget brand and hedge your bets, it could affect you negatively. Cheaper boilers can cost less because they have a shorter warranty and lack legacy support for spare parts.

Saving money with your new boiler

We’ve spoken a lot about spending money in this guide, but now it’s time to talk a little about potentially saving money with a new boiler.

We always advise people to ask for three independent quotes when looking to purchase a boiler.

Shop around for quotes

No two heating installers will provide you with the same quote, so it’s a really good idea to shop around. While it’s not always best to go with the absolute cheapest engineer, it’s good to have prices to compare and options so that you can choose the engineer who’s most suited for you. We always recommend that you get at least three independent quotes when purchasing a new boiler.

Efficiency saving

Newer boilers are more efficient than their older counterparts, so while the cost of a boiler may be a big initial outlay, you could actually reduce your heating bills by upto 30%. This will help you relax, knowing that your warm home is costing you a bit less and saving energy.

Warranty

We’ve already mentioned warranties as an additional cost, but they really are worth having. Should something go wrong with your boiler, the warranty could mean that you’re completely covered without having to pay a thing, not even an excess or call out charge.

Life expectancy

It’s likely that a premium, quality boiler will last longer than its cheaper counterparts. Manufacturers that use high-quality components, such as stainless steel heat exchangers, have a higher confidence in the lifetime expectancy of the product, usually resulting in longer manufacturer warranties.

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