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Full Boiler Replacement Guide

Full Boiler Replacement Guide 2021

When to replace a boiler?

Most combi boilers on the market have a working lifespan of around 10 – 15 years. If your unit is coming close to this age it may be worth considering getting your boiler replaced. Under the ECO3 initiative households that meet certain criteria can get access to a boiler replacement grant – find out more about a boiler grant here. 

Energy Bills Increasing

As boilers age they will tend to lose their efficiency. If you have noticed that your energy bills are increasing month to month then your boiler could be at fault. If this is the case then you may want to consider a boiler replacement. 

It is also important to ensure that your boiler is regularly maintained. Sludge can build up in the boiler and this will require cleaning to get rid of it. Boiler sludge can also add to the cost of your bills as it requires your boiler to work harder to make the same amount of heat. 

Most modern boilers are incredibly energy efficient and are awarded A grades for efficiency. Replacing your old boiler with a brand new A-rated boiler will decrease your energy bills by a significant amount. Using smart thermostats such as Nest with a new A-rated boiler will increase the efficiency even further! 

Consistent Breakdowns

If you have had to call out an engineer more than once in the last year then it may be worth considering replacing your boiler. If the cost of getting the boiler repaired is greater than the cost of a new boiler then it will be economically viable to get a new A-rated boiler installed in your property. Research carried out by showed that over a 6 month period it is likely that a homeowner will spend between £500 to £1000 on an old boiler across multiple breakdowns. 

No longer meeting your needs 

If you have noticed that your boiler is struggling to meet the hot water and heating demands of your home then it may be a sign that you require a boiler with a higher kW output. 

Your boiler is leaking

A boiler that is leaking is never a good sign. In most cases this will actually indicate that there is a crucial issue with an internal component within the boiler, that must get fixed. Any fix on an internal component is going to be expensive – if your heat exchanger has completely failed it will be cheaper in the long run to replace the boiler outright. 

Your boiler smells

If you smell an eggy odour from your boiler then this will most likely signify a gas leak. Immediately turn off your gas meter in your property and call the emergency gas line on 0800 111 999. Then get in touch with a registered Gas Safe engineer. Do this if you ever detect any unusual smells emanating from your boiler.

How much does it cost to replace a boiler?

The costs for a boiler replacement will vary depending on the quality of brand that you choose, however you can expect a boiler replacement to cost between £1800 to £4000.

More technically advanced boilers, such as the Viessmann brand, will generally be on the higher end of that cost bracket. 

Below you will find an estimated cost of a gas boiler replacement in a typical 3 bedroom house. Keep in mind that the estimates may vary based on the boiler type, installation work required and rates that the installers charge. 

Boiler Type

Average cost of boiler excluding installation

Average labour cost of boiler installation

Approximate total cost of boiler fully installed


£600- £2,000


£1,200 – £3,000


£500 – £2,000

£500 – £1,000

£1,000 – £3,500


£500 – £2,750

£500 – £1,000

£1,000 – £3,750

central heating boiler grants

Things to consider before replacing a boiler

Replacing your old boiler with a new one will require a bit of research. You will firstly need to find out what type of fuel your boiler runs on, which boiler model will suit your home and then the best boiler size in terms of a kW output rating for your heating and hot water. 

What size boiler do you need?

Choosing the right size boiler for your home can be a confusing task. Below is a table designed to help you make sense of the different power ratings a boiler has and which would be best suited to your home. Normal boilers that are used in everyday homes have an output rating anywhere between 24 kW and 42 kW.

Property Size

Output Rating

1-2 bedroom, 10 radiators, 1 bathroom


3-4 bedroom, 15 radiators, 1-2 bathroom


4+ bedroom, 20 radiators, 2+ bathroom

35-42kW or storage combi

Fuel Types

Gas Boilers – Gas as the source of fuel for a boiler is around 3 to 4 times cheaper per kWh than other fuels which makes it a relatively cheap fossil fuel to heat your home. The only caveat is that the boiler requires a connection to the gas network. This can incur a cost for first time grid connections. 

Oil Boilers – In rural areas or in homes not connected to the gas networks, installing an oil boiler can work out a more cost effective solution. It is worth noting that the initial installation cost and ongoing maintenance and servicing can make this fuel type more expensive than gas or an LPG boiler. Oil boilers require the oil to be stored in a tank on your property

LPG Boilers – An LPG boiler works in a very similar way to both natural gas and oil boilers. The boiler will burn the fuel to produce the energy needed to heat water from the mains supply.

Which fuel does my boiler use?

If you are already living in a property where you are looking to replace your boiler then you will most likely already know what type of fuel you have. If you are looking to purchase a new home then it is wise to check what type of fuel the current boiler uses. The EPC register will give you the information you need to find out which fuel type your boiler uses.

Where to put your boiler

Boilers can be somewhat unsightly so it is worth bearing in mind that the location of your boiler can change the overall look of a room. Make sure to choose a spot you are happy with as it will be up there for at least 10 years!

In most cases the kitchen is the most popular location for a boiler and it is a good idea to get this boxed in using the same style cabinets as the rest of the kitchen, this keeps your boiler out of sight and doesn’t make it an eyesore. If space is at a premium in your kitchen then we recommend looking to get your boiler installed in an airing cupboard or a garage, if you have one. 

We always recommend leaving your boiler in its current location as this will emit any cost of having to relocate it. If the boiler is in a bedroom for example then we would advise you to look at getting this moved as it could increase the market interest of your home if you come to sell your property. 

Cost of moving a boiler

Moving a conventional combi boiler can cost in the range of £300 to £800 on average and will usually take 1 – 2 days to be installed. These costs can range depending on the amount of work involved in moving them.

How much is a boiler installation?

The cost of installing a boiler can vary depending on the complexity of the work being carried out.  You want to gauge the cost based on two scenarios – replacing a boiler in its current location and the cost for installing a boiler in a new location.

Installation of a new combi boiler

Approx cost with mid range boiler

Time taken

1) Replacing an existing combi boiler with a new boiler


1 Day

2) Replacing an existing combi boiler with a new boiler


1-2 days

How much can you save from replacing your old boiler?

Replacing your old boiler for a new, more energy efficient boiler will save you money every year that it is in use. This will then add up to a bulk saving over the lifetime of the boilers usage. The Energy Savings Trust states that you can save up to £350 a year by replacing your old inefficient boiler with a new A-rated boiler.

Efficiency of old boiler

% saving

£ saving













The more inefficient your current boiler is, the more that you can save by replacing it. Replacing your old boiler will also help you avoid any breakdown cots. Newer A-rated boilers, as we have discussed, are incredibly energy efficient but you can further increase this efficiency by using smart thermostats to manage the usage of the boiler at times when it is only necessary. 

Buying a boiler

The initial cost of a boiler can vary depending on the type of boiler that your property needs. The capacity and the efficiency rating all have an impact on the cost of the boiler. There is the general notion in the marketplace that A-rated boiler cost more than their lower efficient counterparts, however, keep in mind that you will save more money on your heating bills in the long run. 

A budget boiler will set you back in the range of £600. Mid priced boiler can cost from around £600 – £850 and should guarantee a life expectancy of 7 to 10 years. Premium boilers can cost £1200 upwards. 

The right type of boiler for your home

There are 3 types of boiler to choose from for your home:

Combi Boiler 

  • Compact size and a great choice for smaller properties
  • No need for separate water tank
  • Installation is cheap 
  • On demand hot water is provided from the mains

System Boiler 

  • Suitable for medium to large homes
  • No need for loft tank which frees up space in the loft
  • Constant feed of hot water to all taps in the property

Conventional Boilers 

  • A great choice for homes with high hot water demand and low mains pressure and flow rate
  • Suitable for houses with two or more bathrooms
  • Requires a cold and hot water tank in the loft

What boiler brands are there to choose from?

There are a large pool of boiler manufacturers to choose from in the UK market making it difficult to understand which one is right for you. Below we have prepared a list of some of the UK’s most popular brands. 


Viessmann have an absolute stellar reputation and are easily classed as the best boiler brand in the UK. As a leader in both technology and patented design these boilers are built to last, boasting high efficiency and amazing reliability. Viessmann offers a warranty up to 10 years. Why not read through our Viessmann vs Worcester Bosch boilers review guide to find out which is best.

Worcester Bosch 

Worcester Bosch has a reputation of delivering high quality products. Their boilers are highly  reviewed and are boasted as being very quiet and highly efficient. Some reviews do however state that the controls are a little confusing to use. Worcester Bosch are considered a top of the range brand so expect to pay a bit more for the name. 


Valliant is another top of the range supplier and the brand name started life over 120 years ago! Again they are not the cheapest option out there but you are buying a quality product who have great reviews online.


Warranties are a big deal for boiler manufacturers and is a big selling point for any homeowner looking to install a new boiler in their property. Worcester Bosch and Viessmann both provide warranties with any purchase of a new boiler.

Worcester Bosch gives you 5 years standard warranty with any new boiler, however, Viessmann beats that by offering anywhere from 7 to 10 years warranty and they also offer a number of discounts if you get the boiler installed by an approved installer.

With that in mind, the Viessmann boiler can offer nearly double the warranty time compared to a Worcester Bosch and as we have discovered, the technology and energy efficiency is far superior.

Michael Cornish

Michael Cornish