Key Takeaways
- The UK has 23 million gas boilers; phase-out may begin by 2035.
- Three main gas boiler types: combi, system, and regular (conventional).
- Combi boilers are compact and best for small to medium homes.
- System boilers suit homes with higher hot water demand.
- Regular boilers work well in homes with low mains pressure.
- All modern boilers use energy-efficient condensing technology.
- Boiler replacement costs vary by type, brand, and installation complexity.
- Combi boilers: cheapest and easiest to install.
- System and regular boilers need additional space and parts.
- Labour and regional pricing impact the total replacement cost.
- Boiler unit prices range from £600 to £4,000.
- Installation typically costs £1,000 to £2,000.
- The average combi boiler replacement is about £3,000.
Currently, it is estimated that there are 23 million gas boilers in the UK. With the UK’s Net Zero Goal set for 2050, it’s reported that gas boiler installations will perhaps be entirely stopped by 2035.
With ten years before this deadline is enforceable, most UK homes will be replacing their older gas boilers with a new one.
However, what is the cost of replacing your gas boiler in 2025?
Before going any further, let’s discuss what type of gas boilers are available to the UK public.
Types Of Gas Boilers
In the UK, there are three main types of gas boilers:
- Combination (Combi) Boilers
- System Boilers
- And Regular/Conventional (Heat Only) Boilers
Each boiler type has been designed to meet specific household heating and hot water needs.
Combi Boilers
Compact in design, combi boilers are perfect for small to medium-sized homes. They heat water on demand and perform two functions: heating the home and providing hot water.
Combi boilers heat water on demand, eliminating the need to install a separate storage tank.
As the UK’s most popular type of boiler, its advantages are:
- Compact and space-saving design
- Provide hot water on demand
- And are incredibly energy-efficient, with all modern units needing an efficiency rating of over 90%
However, their main limitations are a reduced ability to supply hot water to multiple outlets simultaneously, and their flow rate relies entirely on the pressure of the mains water supply.
System Boilers
System boilers heat water from the mains and store it in a separate hot water cylinder, ensuring a steady supply to multiple taps.
Perfect for medium to large homes where hot water demand can be high.
There are several advantages to having a system boiler, which include:
- Can handle high hot water demand.
- No need for a cold water tank in the loft.
- Compatible with solar water heating systems.
While system boilers will require more space for their hot water cylinder, it’s also worth noting that the hot water isn’t instant and will require homeowners to wait.
Regular/Conventional (Heat Only) Boilers
Regular boilers use a cold water tank (usually in the loft) and a hot water cylinder to provide heating and hot water. They are usually found in older homes with traditional heating systems and high hot water usage.
Their advantages are:
- They are suitable for areas with low mains water pressure.
- Can supply hot water to multiple outlets simultaneously.
- And are compatible with older radiator systems.
However, a regular boiler will need more space for the addition of tanks and cylinders and will require the homeowners to wait for hot water.
All of the above gas boilers now use condensing technology to comply with UK efficiency regulations. Condensing technology is more energy-efficient because it captures and reuses heat from exhaust gases.
Now that we know what boilers are available to the UK public, what factors will affect the overall price tag?
Factors That Affect The Cost Of A Replacement Gas Boiler
The cost of replacing a gas boiler can vary significantly depending on several key elements.
Understanding these cost drivers can help you make an informed choice and avoid unexpected expenses:
Boiler Type
The type of gas boiler you’re replacing your old unit with will directly affect its cost. In general, a combi boiler is usually the most affordable option. They are compact and easy to install, especially if it is a swap-out.
While the system and regular boiler will be a bit more expensive, this is because these units require additional components to work.
Boiler Brand And Model
The boiler brand you choose will directly affect costs. Premium brands such as Worcester Bosch, Vaillant, Viessmann cost more but often come with longer warranties and better customer support.
Budget brands can be cheaper upfront but may have shorter lifespans or fewer features.
Also, depending on whether you’d like a more comprehensive warranty, you may be required to pay more. However, longer warranties do provide homeowners with peace of mind.
Size And Output
All gas boilers will be labelled with their size and power, which is measured in kilowatts (kW). Higher kW ratings mean the boiler can heat more water quickly, but generally cost more.
Larger homes usually require more hot water, so they need a more powerful (and expensive) boiler.
Installation Complexity
If you’re planning on a straight swap, you’ll be cutting down on costs. However, if you’re planning on:
- Upgrading the boiler and pipelines
- Changing your boiler type
- Or relocating its spot
Expect the costs to increase due to labour, and if you need to install new components or materials.
Additional components and materials you may need include:
- A new flue or vertical flue kit
- Magnetic filters to protect the system
- Smart thermostats or controls
- Hot water cylinders (for system or regular boilers)
Always check if your Gas Safe registered engineer’s quote includes removing and disposing of your old boiler, as sometimes this is an extra expense.
Lastly, labour costs vary across the UK. However, installations in London and the South East tend to be more expensive than in other regions.
Average Costs Of A Replacement Gas Boiler 2025
According to our new associates, Checkatrade, the average costs for gas boilers are as follows:
Combi Boiler Costs
A straightforward replacement of your old combi boiler with a new model in the exact location can cost between £2,500 and £4,000 (supply and installation).
Installation costs are estimated to be between £1,000 and £2,000.
Homeowners looking to replace their old combi boiler with a system or regular unit can expect it to cost around £4,000 (supply and installation).
On average, homeowners can expect to pay around £3,000 for a combi boiler replacement.
System Boiler Costs
The average cost of upgrading to a new gas system boiler is estimated to be £3,000, while the unit itself costs around £1,500.
Installation costs are estimated to be between £1,000 and £2,000.
Regular/Conventional Boiler Costs
On average, a conventional boiler will set you back around £3,000 (supply and installation), while the unit retails for around £1,500.
Installation costs are estimated to be between £1,000 and £2,000.
For quick reference, see the table below:
| Boiler Type | Unit Cost | Installation Cost | Total Cost |
|---|---|---|---|
| Combi | £600 – £4,000 | £1,000 – £2,000 | £1,600 – £6,000 |
| System Boiler | £600 – £3,000 | £1,000 – £2,000 | £1,600 – £5,000 |
| Regular/Conventional | £600 – £3,500 | £1,000 – £2,000 | £1,600 – £5,500 |
If you’re ready to replace your gas boiler, WarmZilla can assist you within 48 hours anywhere in the UK with no hidden costs.
Replace Your Old Gas Boiler With No Hidden Costs
At WarmZilla, we’re dedicated to making buying a boiler as simple as possible.
The first step is to complete our simple-to-understand survey. Once completed, you’ll be served boiler options that are perfect for your home.
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