Replacing an old boiler with a new combi or system boiler is a great way to save money on your gas bills and reduce costs on breakdowns. Older boilers, particularly those over 10 years old, are a lot less efficient - often around 60-70%. In contrast, modern condensing combi and system boilers typically achieve efficiencies of over 90%, together with improved reliability and some with 10 year manufacturers' warranties.
Over the course of a year, many households find that the reduction in energy usage results in substantial financial savings, helping to offset the initial installation cost of a new boiler within 3 to 4 years.
In addition to lower energy bills, a new boiler also reduces maintenance and repair expenses. Older systems are more prone to breakdowns, and replacement parts can be expensive or difficult to source. Frequent callouts and repairs quickly add up, making an aging boiler increasingly costly to maintain. A new combi or system boiler, on the other hand, is far more reliable and typically comes with a manufacturer’s warranty, providing peace of mind and protection against unexpected costs.
Combi boilers can also eliminate the need for separate hot water tanks, reducing heat loss from stored water and further improving efficiency. System boilers, while retaining a cylinder, are still designed to minimise energy waste and operate more economically than older systems.
A combi boiler is a compact heating system that provides central heating and hot water from a single unit. Unlike traditional gravity fed systems, it doesn’t require a separate hot water cylinder or cold water storage tank. Instead, it heats water directly from the mains supply whenever you turn on a tap or shower, delivering hot water instantly and only when you need it.
One of the main reasons to choose a combi boiler is cost efficiency. Because it heats water on demand, there’s no energy wasted keeping a tank of water hot throughout the day. This makes it more efficient than older systems and can lead to noticeable savings on your energy bills—especially important with rising energy costs.
Another major advantage is space saving. Combi boilers are ideal if you live in a smaller home, flat, or property where space is limited. By removing the need for bulky tanks in the loft or airing cupboard, you free up valuable storage or living space.
Combi boilers also offer convenience and performance. You get hot water instantly, without waiting around for a tank to heat up, and you won’t run out of hot water in the traditional sense. With adequate mains water pressure, they also improve shower performance, doing away with noisy shower pumps from gravity fed systems.
On top of that, modern combi boilers are very reliable and often come with long 10 year warranties, giving you peace of mind and reducing the likelihood of costly repairs.
A system boiler is a central heating system that provides heating and hot water using a separate hot water cylinder. Unlike gravity fed traditional (regular) systems, it doesn’t require a cold water tank in the loft. The circulation pump and expansion vessel (to balance the pressure) are built into the boiler itself, making it more compact and efficient than older setups.
With a system boiler, water is heated and stored in a cylinder, so it’s ready to be used whenever you need it. This makes it particularly well suited to homes with higher hot water demand, such as properties with multiple bathrooms. Unlike the combi boiler above, a system boiler can supply hot water to multiple outlets simultaneously without a major drop in pressure or temperature.
One of the main reasons to choose a system boiler is reliable performance. Because hot water is stored, you get consistent flow and pressure, making showers, baths, and taps run more smoothly—even during busy periods in the home.
Modern system boilers are designed to minimise heat loss from the system, and because they work with stored hot water, they can be paired with energy-saving features like insulated cylinders and smart controls to help reduce energy usage and lower bills.
Another advantage is compatibility with renewable energy systems, such as solar thermal panels. This can further improve efficiency and reduce long-term energy costs.
Installation is generally simpler than older conventional systems since fewer external components are needed, and maintenance is often easier as well.
In short, a system boiler is a powerful, efficient, and dependable heating system, especially for larger households where multiple people need hot water at the same time.
So now you know which type of boiler is suitable for your home, who is manufacturing the most efficient and reliable boiler for the right price? We have compiled a list below with average online boiler prices for 2026.
Each boiler comes with a kW rating depending on the size of your home and heating requirements so it is best to talk to your Gas Safe engineer to discuss which boiler is best for your home.
Choosing the best boiler comes down to a few key factors: efficiency (up to 98% for a combi), reliability, warranty, and kW power. Modern boilers are A-rated, but the best ones stand out for build quality, long warranties, and consistent performance.
Power ratings (kW) indicate the size and output of the boiler, the larger the boiler the bigger the household.
Exceptional build quality and long-term reliability.
Most popular brand in the UK and known for dependability and nationwide support.
A premium choice often recommended for larger homes and high hot water demand.
A heating engineer will take between 1 and 3 days to install a boiler depending on the complexity. For a swap that doesn't require and modifications and is a like for like replacement expect to pay a day rate.
An engineer has to inspect and sign off the installation after fitting and will probably account for this in his quote.
Installations cost between £600 and £2,000.