New Boiler Cost: Combi, System and Regular Boilers Explained

Combi, system and regular boilers explained

A combi boiler heats water directly from the mains on demand, so there is no need for a hot water cylinder or a cold water tank in the loft. This makes combis a popular choice for flats and smaller to medium homes where space is at a premium and hot water demand is not too high, for example one bathroom and a kitchen.

A system boiler works with a hot water cylinder but does not need a separate cold water tank, since most of the components are built into the boiler itself. This suits homes with a bit more hot water demand, such as a family bathroom plus an en suite, where running two outlets at once would strain a combi.

A regular, or conventional, boiler uses both a hot water cylinder and a cold water storage tank, usually in the loft. These are common in older properties that already have this setup, and are often the simplest like-for-like swap where the pipework and cylinder are already in place.

What affects the cost of a new boiler installation

The boiler unit itself is only part of the overall cost. Labour, any pipework alterations, flue routing, and whether you are switching boiler type all have a significant impact. A straightforward like-for-like combi swap in roughly the same spot is generally the most cost-effective job, because the existing pipework, gas supply and flue can often be reused.

Switching from a regular or system boiler to a combi, or moving the boiler to a different room, tends to cost more because it involves rerouting pipework, removing a redundant cylinder and tank, and sometimes upgrading the gas supply pipe to cope with a combi's higher instantaneous demand.

Other factors include the size and output of the boiler needed for your property, whether a magnetic filter and scale reducer are being fitted (which we would always recommend), and any additional controls such as a smart thermostat or a wireless room stat.

Typical indicative cost ranges

As a general and purely indicative guide, a straightforward combi-to-combi swap in a small to medium home might sit somewhere in the region of £2,000-£3,500 including installation, while a system or regular boiler replacement, or a more involved combi conversion, can range from £3,000 up to £5,500 or more depending on the scope of work.

These figures will vary depending on the specific property, the boiler brand and output chosen, and any additional work such as relocating radiators or upgrading pipework. A proper site visit and written quotation is always the best way to get an accurate figure for your own home, and we would always recommend being wary of any quote given without someone actually seeing the installation.

Choosing the right size and brand

Boiler output is measured in kW, and choosing the correct size matters more than most people realise. A boiler that is too small will struggle to keep up with demand, particularly for hot water, while an oversized boiler can be less efficient and more expensive than necessary. A competent engineer will calculate this based on the number of bathrooms, radiators and the property's heat loss, not just guess based on the old boiler's rating.

We install Viessmann and Grant boilers, both well-regarded brands known for reliability and efficient performance. Viessmann in particular has a strong reputation for build quality, while Grant is often a good fit for oil-fired heating systems common in some rural parts of Hertfordshire that are not on the mains gas network.

Warranties and what they cover

One of the real advantages of a new boiler is the warranty that comes with it. When installed and registered correctly by a qualified installer, Viessmann and Grant boilers can carry warranties of up to 10 years, covering parts and in many cases labour for manufacturing faults during that period.

To keep a long warranty valid, most manufacturers require the boiler to be serviced annually by a Gas Safe registered engineer, and often that a suitable magnetic filter is fitted at the time of installation. It is well worth keeping your service records and installation paperwork somewhere safe, as you will need them if you ever need to make a warranty claim.

Planning your installation

A typical straightforward boiler swap can usually be completed in a single day, while more involved jobs such as a conversion from a regular boiler to a combi, or a boiler relocation, may take two days. Your installer should talk you through what to expect, including a period without heating or hot water while the old boiler is disconnected and the new one is fitted, tested and commissioned.

After installation, you should receive a benchmark checklist confirming the boiler has been commissioned correctly, along with building control notification (usually handled via the Gas Safe scheme) and your warranty registration. If any of this is missing, it is worth asking your installer to confirm it has been done.

Frequently asked questions

How much does a new boiler cost in the UK?

As an indicative guide only, a like-for-like combi swap often falls somewhere between £2,000-£3,500, while a system or regular boiler replacement or a boiler conversion can range from £3,000-£5,500 or more. A site visit is the only way to get an accurate price for your home.

Which type of boiler is best for my home?

It depends on your hot water demand and existing setup. A combi suits smaller households with lower demand, a system boiler suits homes needing more hot water at once, and a regular boiler suits larger properties that already have a cylinder and tank in place.

How long does a new boiler installation take?

A straightforward like-for-like swap usually takes a single day. A conversion between boiler types, or relocating the boiler to a new position, can take a day or two depending on the pipework and flue changes needed.

What warranty comes with a new boiler?

This depends on the brand and model, but Viessmann and Grant boilers, which we install, can carry warranties of up to 10 years when installed and registered correctly, provided the boiler is serviced annually as required.

Do you install boilers across Hertfordshire?

Yes, we install new boilers across Harpenden, St Albans and the wider Hertfordshire area, and can arrange a site visit to give you an accurate, no-obligation quotation.