What Is the Average Cost of Replacing a Gas Boiler?

With around 23 million gas boilers still heating UK homes, gas remains the most common heating fuel nationwide.

Per kilowatt hour, using natural gas to heat your home and water is still the cheapest fuel.

According to Ofgem, the energy price cap for gas from 1 July to 30 September 2025 is 6.33p per kWh, with a daily standing charge of 29.82p.

By comparison, electricity costs 25.73p per kWh, with a daily standing charge of 51.37p.

For those looking to replace their gas boiler with a more economical unit, what is the average cost of replacing a gas boiler in 2025?

Before we get ahead of ourselves, you need to know what type of gas boilers there are in the UK.

Type of Gas Boilers In The UK

Before we break down costs, it’s essential to understand the three main types of gas boilers available today:

1. Combi Boilers (Combination Boilers)

Combi boilers are compact and are the most popular type of boiler in the UK.

Designed for small to medium-sized homes, it combines central heating and hot water functionality, which is key to its popularity.

Its main selling points are:

• Providing hot water and heating on demand
• No hot water cylinder or storage tank needed
• And are energy-efficient while being space-saving

However, nothing is perfect, meaning combi boilers can struggle to supply multiple hot water outlets simultaneously.

Combi boilers rely on mains water pressure, which may require a pump in low-pressure areas.

2. System Boilers

System boilers require more space than combi boilers.

However, they store hot water in a separate cylinder, making them suitable for homes with higher hot water demands.

Their size makes them great for larger homes with multiple bathrooms.

System boilers are also compatible with solar water heating systems, helping to offset the use of fossil fuels.

They don’t require a loft tank, making them easier to install in modern homes.

However, it should be noted that the hot water supply is not instant, and heated stored water can run out.

Also, a system boiler does require more space for the cylinder.

3. Regular (Conventional) Boilers

Regular boilers are usually found in older properties.

They also use a cold water tank (usually in the loft) and a hot water cylinder, which requires more space.

A significant benefit of a regular boiler system is its suitability for homes with low water pressure.

Regular boilers can supply multiple taps simultaneously and are compatible with traditional heating systems.

While these boilers require more space, it should be mentioned that hot water is not available on demand because the heated water is stored.

Now that we understand the different types of gas boilers, what affects the average cost of replacing one?

What Affects the Cost of a Gas Boiler Replacement?

Replacing a boiler isn’t a one-size-fits-all scenario.

Several factors influence the total cost:

Boiler Type

Combi boilers are generally the most affordable units.

This is due to a more straightforward installation process.

System and regular boilers involve more components, making them pricier.

Brand and Model

Premium brands like Worcester Bosch, Vaillant, and Viessmann often cost more upfront but offer more extended warranties and better reliability.

Budget brands are more affordable upfront but may have shorter lifespans and higher maintenance costs.

Boiler Size (Output)

Your boiler’s power is measured in kilowatts (kW).

The size of your boiler will directly affect how much water the boiler can heat.

Generally, larger homes usually require higher-output (and more expensive) models.

Installation Complexity

Straight swaps in the exact location usually mean cheaper installation.

But costs rise if you’re:

• Switching boiler types
• Relocating the boiler
• And upgrading your heating system

Also, new items may be needed, which will cost more.

These additional costs may include:

• New flues
• Magnetic filters
• Smart thermostats
• And even the addition of hot water cylinders

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.

Labour Costs

Labour rates vary by region. You can expect to pay more in London and the South East than in northern areas.

Get at least three quotes to compare pricing and potentially lower labour costs.

Now that we’ve reviewed the cost factors, here are the average installation costs for 2025.

Average Boiler Replacement Costs In 2025

According to our new associates, Checkatrade, the average costs for gas boilers are as follows:

The following table:

For a simple combi boiler swap, it can typically cost between £2,500 and £4,000, averaging around £3,000

While system or regular upgrades can exceed £4,000, depending on system changes.

If you’re ready to install a new boiler and need a fast turnaround, who can help?

Need a Fast Boiler Replacement?

At WarmZilla, we ensure that boiler replacement is hassle-free.

With our streamlined online boiler survey, you can get a new boiler installed within 48 hours, with no hidden costs.

Here’s how it works:

• Complete a short survey about your home and heating needs
• Receive instant quotes tailored to your property
• Book installation at a time that suits you

We only use Gas Safe registered engineers and offer flexible finance options on a wide range of trusted brands.