So your 15 year old gas boiler has broken down again and is on its last legs and you can’t face spending money on repairs again. It’s finally time to start thinking about replacing it but you have no idea what it’s going to cost as the last time you bought a new boiler is a hazy distant memory.
This guide to gas boiler replacement costs will arm you with more knowledge to make the task of replacing your central heating system a little less daunting.
1: Establish what heating system you have now
There are three main heating systems you may have:
- Combination boiler
- Gravity fed system with separate hot water cylinder
- High pressure (unvented) system with separate hot water cylinder.
How do you identify which system you have? Well if your hot water is heated by the gas boiler for immediate use and you don’t have a hot water cylinder then you are likely to have a combination boiler or “combi”. If you do have a hot water cylinder then the gravity fed system can be identified if you have a cold water tank and an expansion overflow tank (often in the loft of a house). High pressure (unvented systems) are less common but do not have tanks in the loft and deliver water at mains pressure.
2: Decide what heating system you want to replace it with
There are three main considerations which may sway your view:
- The system you currently have and its hot water delivery
- The difficulty of upgrading to a condensing boiler
- Solar options for water heating
If you already have a combination boiler and you are happy with its overall performance then a like-for-like replacement is a good option. Depending on the output of your old boiler you may wish to consider increasing the boiler size if you want to boost the hot water supply for a more powerful shower. Combination boilers of 30kW and upwards are now available.
Gravity fed boilers
For gravity fed central heating systems the choice becomes more complex. Few heating engineers these days would recommend a gravity fed system for a completely new installation as they have some limitations – not least a cold water tank in the loft that has the potential to burst and cause water damage. However if you are on a budget and happy with the heating system then a like-for like replacement is certainly a realistic option. For flats and 1-2 bedroom houses where the hot water consumption is relatively low then a combination gas boiler can also be a very good option. Replacing a gravity system with a combi is usually quite straightforward and can free up the space where the hot water cylinder is sited.
There are two sorts of boiler that can be used when replacing: system boilers and heat only boilers. Many older boiler systems have external pumps to move the heated water around and for these a heat only boiler can be used. A system boiler has the pump built into the boiler itself, which reduces the plumbing an installer is required to do but it does increase the cost of the boiler. So if the rest of your system is fine then a heat only boiler can be a good option whereas if you need to replace other elements it may be worth considering a system boiler instead.
High pressure (unvented) systems
These are generally installed in larger houses where the hot water demands of a large family may outstrip a combination boiler’s capacity. Generally they would be replaced like-for-like although the same consideration needs to be given to whether a system boiler or a heat only boiler is the better option. Your heating engineer can guide you on this.
Almost all new boilers supplied since 2003 have been of the more fuel efficient condensing type. These have efficiencies of 90% upwards and are ‘A’ rated. Older boilers can often be G rated or 50-70% efficient so by switching to a condensing boiler you should save money on your fuel bills.
The downside of a condensing boiler is that it produces a small but steady stream of water which needs to be drained away. A condensing boiler needs access to a drain either internally (ideally) or externally. Depending on the position of your boiler this can be easy to do or practically impossible. Where it is difficult to do it may be worth considering moving the boiler position rather than incurring unnecessary extra cost. As the system will need to be adjusted by re-siting the boiler it may also lead you to decide to switch boiler types. More likely, you will have to add a condensate pump to pump the waste water to the nearest drain outlet. It is important that the condensate pipe is not allowed to freeze so if it drains to the outside it should be insulated.
There are limited governments grants available for those replacing a non-condensing boiler. Read more about boiler grants.
Solar Water Heating
If you are looking to replace the hot water cylinder on your gravity fed or high pressure system hot water and like the idea of using solar water heating then it’s also worth thinking about a twin coil hot water cylinder. These cylinders can connect to a conventional gas boiler as well as a solar heated flow from a solar water heating panel. When the sun is shining then the hot water is heated for free (in the Summer 80-90% of your hot water needs can be covered). In the winter the heat from the sun needs to be topped up with your gas boiler (probably only 20-30% of your hot water needs will be covered by solar). Solar water heating systems do add quite a cost to the system but you can offset some of the cost with the savings in fuel you will make. In addition, there is a government scheme, the Renewable Heat Initiative (RHI), which pays 19.51p per kWh of heat produced. That means the government pays you, for 7 years, every time you heat hot water using solar water heating panels.
Nowadays solar PV panels for generating electricity are quite popular. Excess electricity is normally exported to the electricity grid but products now exist to divert this extra energy into an immersion heater which is used to heat your hot water.
See solar panels for more details on solar systems. If you plan to use solar water heating in the future you may steer away from switching to a combination boiler.
4: Changes In Boiler Installation
Over the years since your last boiler installation, standards may have changed. A few areas that are worth being aware of:
- Gas Supply Pipes
- Boiler Flue Requirements
- Condensate Drain Pipe
Gas Supply Pipes
Changes in gas regulations mean that 15mm gas supply pipes may need upgrading to 22mm or even 28mm. The installer should measure the pressure drop between the gas meter and the boiler and if it is too great, or the supply pressure is below the boiler manufacturers minimum operating pressure, the supply pipe will need to be upgraded. If the pressure is too low there may be problems when different gas appliances are operated at the same time. It’s part of the responsibility of the installer to ensure this is correct. If you are switching to a higher output boiler you may also need to upgrade the supply pipe.
Boiler Flue Requirements
Increased safety concerns mean that some older types of boiler flue arrangement may no longer be permitted as they do not meet current industry guidelines. This may require the boiler flue to be modified or replaced.
Condensate Drain Pipe
As highlighted above under condensing boilers, modern condensing boilers require a drain outlet for the condensed liquid they produce. When replacing an older non-condensing boiler a new condensate drain pipe will have to be added. Even if a condensate pipe is fitted, experience has shown that it could be at risk of freezing and the installer may well want to increase its size and ensure that it is properly lagged.
4: What’s A New Boiler Going To Cost?
Well now you have a better view of what system you want, let’s try and get a better idea of the gas boiler replacement cost. There are some general costs and a number of costs that depend on the state of the current system.
Below are some broad costs for various elements of the replacement:
|Replacement boiler||Typical cost|
| Replace existing boiler with
new boiler in existing position
on make and model
|Heating engineer labour||£500-£1,000|
Heating Upgrade Options
|Heating Option||Typical cost|
|Adding a magnetic filtration system||£120|
|Powerflushing 10 radiators||£300|
|Adding new radiators||£70-£150 per radiator
depending on size & position
|New wireless programmer and thermostat||£180|
|Adding Thermostatic Radiator Valves (TRVs)||£20 per radiator|
|New hot water cylinder (120 litre)||£250-£300|
|New hot water cylinder (250 litre solar compatible)||£800-£1,000|
Depending on current installation
- Upgrade gas supply pipe from meter to boiler to larger diameter pipe: £120-200
- Upgrading boiler flue to current standards: £250-£400
- Install condensate drain pipe: £150-£250
- Condensate pump, if access to a drain from the boiler is difficult: £100
Do agree with the installer, ideally in writing when he quotes for the work, what they are going to do to cover the impact on things like:
- room decoration
- where any pipes or cables run; i.e. will they be visible and how will they be fixed to the wall; are they going to be painted or boxed in?
- what “making good” will the installer be doing when drilling through walls or ceilings
- when running condensate pipes to the outside how will the pipe be insulated; where any brickwork or paving slabs have to be lifted how are they going to be re-instated?
4: What next?
The next step is to get two or three estimates from local installers you trust so you can compare their gas boiler prices. Ask family or friends for recommendations. Ask for itemised quotations so you can make a fair comparison. See Boiler Upgrades Explained.
If you want a more specific indication of what you may pay then use our replacement boiler cost online calculator. You can then compare any quotations from installers with our guideline estimate.
If you want a quick way to get quotes from local installers using the Boiler Guide service then click here.