New Boiler Guide 2026: How to Choose the Right Boiler

Choosing a new boiler can feel more complicated than it needs to be. This new boiler guide explains what I would actually look at before choosing a boiler for a UK home, including boiler type, hot-water demand, output, controls, warranty and installation.

How many bathrooms do you have? How much hot water does the household use? Do you already have a hot-water cylinder? What is the incoming water flow like? And is there actually a good reason to change the type of heating system you already have?

Once those questions are answered, choosing a suitable new boiler becomes much easier.

Quick Answer

For many smaller and medium-sized homes with one bathroom, a combi boiler is usually the simplest option because it provides heating and hot water without a separate cylinder.

For larger homes with higher hot-water demand or two bathrooms being used at the same time, a system boiler with a hot-water cylinder may be more suitable. The right choice depends on your property, water flow and how your household uses hot water.

🔑 Key Points

• Choose the right boiler type before comparing individual brands and models.
• Combi boilers suit many one-bathroom homes, but they are not automatically the best choice for every property.
• System boilers with stored hot water can work better where hot-water demand is higher.
• You do not automatically need to convert a regular boiler to a combi.
• Boiler output should be matched to what the property actually needs.
• Incoming mains-water performance is particularly important when choosing a combi boiler.
• Compare the whole installation, controls, warranty and aftercare rather than only the appliance price.

New Boiler Guide: The 3 Main Boiler Types

Most UK homes use one of three main boiler arrangements: combi, system or regular. Choosing the right type first is more useful than immediately comparing brands.

If you are unsure which system you already have, start with what type of boiler do I have?

You can also compare the arrangements in our guide to the different types of boiler systems.

Is a Combi Boiler Right for Your Home?

A combi boiler provides heating and heats hot water directly when you open a tap. It does not normally need a separate hot-water cylinder.

That makes combis particularly useful where space is limited.

• No separate hot-water cylinder
• Hot water produced on demand
• Compact heating arrangement
• Often suitable for homes with one bathroom

The incoming water supply matters as well. A more powerful combi cannot create water flow that is not available from the mains.

If the incoming supply is poor, simply fitting the biggest combi available will not automatically give you a stronger shower.

If a combi looks suitable for your home, compare our best combi boilers.

When Is a System Boiler Better?

A system boiler works with a separate hot-water cylinder.

Stored hot water can make more sense where several people may need hot water at around the same time.

For example, if two showers are regularly used together, I would not automatically recommend a combi simply because it saves cylinder space.

The household’s actual demand, incoming water supply, cylinder size and existing heating system should all be considered.

If you already have this arrangement, keeping it may be simpler than redesigning the whole system. See our system boiler replacement page.

You can also compare manufacturers in our best system boiler brands guide.

When Does a Regular Boiler Still Make Sense?

A regular boiler, sometimes called a heat-only boiler, is still found in many UK homes.

Homeowners sometimes assume an older regular boiler system should automatically be converted to a combi. I would not make that decision based on age alone.

If the cylinder, controls, radiators and pipework are suitable and the system works well for the household, a like-for-like boiler replacement can still make sense.

A conversion is worth considering when it gives you a genuine benefit rather than simply because a combi is a different type of boiler.

If you are considering changing the system, read our guide to replacing a regular boiler with a combi.

What Size Boiler Do I Need?

Boiler size is usually shown in kilowatts, or kW, but I would not choose a boiler simply from the number of bedrooms.

The heating output should be based on what the property actually needs.

• Property size
• Heat loss
• Insulation
• Number and size of radiators
• Number of bathrooms
• Hot-water demand
• Incoming mains-water performance when choosing a combi

Oversizing is not automatically an upgrade. A boiler should work properly with the heating system rather than simply having the highest output on the specification sheet.

Why Can Combi Boiler kW Be Confusing?

With a combi boiler there are two different demands to consider: heating the property and producing hot water.

The home may need a relatively modest amount of power for its radiators, while producing hot water quickly for taps or a shower can require a much higher output.

This is why a combi may be advertised as 30kW or 35kW even though the property’s actual space-heating requirement is considerably lower.

Which Boiler Brand Should I Choose?

There is no single boiler manufacturer that is automatically the best choice for every home.

I would compare the individual model and how well it suits the property rather than choosing purely from the badge on the front.

• Suitable heating output
• Hot-water performance
• Physical size
• Compatible heating controls
• Warranty or guarantee terms
• Parts availability
• Manufacturer support
• Servicing requirements

If you want to compare models and manufacturers, see our best boilers in the UK guide.

How Important Is the Boiler Warranty?

As part of this new boiler guide, I would also look beyond the headline warranty length.

Check what the warranty or guarantee covers and the conditions you need to follow. Manufacturer terms may include correct installation, registration, system protection and ongoing servicing requirements.

See our boiler warranty guide for more detail.

How Much Does a New Boiler Cost?

The boiler itself is only part of the installation price. The existing system, boiler position, controls, flue, pipework and any system alterations can all affect the final quotation.

I would compare the complete installation rather than simply looking for the cheapest boiler.

For a detailed breakdown and our current package prices, see the new boiler cost guide.

For independent UK context, the Energy Saving Trust boiler guide currently gives an average figure of £3,500 for replacing a gas boiler in Great Britain with an A-rated boiler and thermostatic radiator valves.

Should I Move My Boiler?

If the existing position is suitable, keeping the boiler where it is will normally make the job simpler.

Moving it may mean altering the gas pipe, heating pipework, condensate route and flue.

That does not mean relocation is a bad idea. It may be worthwhile if it improves access, frees up useful space or works better with renovation plans.

Read our guide to boiler relocation costs if you are considering a new location.

What About Replacing a Back Boiler?

Replacing a back boiler is normally more involved than replacing a modern wall-hung boiler in the same position.

A suitable new boiler location normally has to be found, and that can mean more pipework and flue alterations.

If this is the system you have, read our back boiler replacement guide.

Do Heating Controls Matter?

Yes. A good boiler with poor controls is still a poorly controlled heating system.

The right controls help you manage when the home is heated and the temperature you actually need. Depending on the system, this may include a room thermostat, programmer, smart controls and thermostatic radiator valves.

Energy Saving Trust also recommends making proper use of heating controls and having boilers serviced regularly to help the system operate effectively. Read Energy Saving Trust’s heating controls advice.

Should I Repair or Replace My Existing Boiler?

Do not replace a boiler simply because it has developed one fault.

If the boiler has otherwise been reliable, the required part is available and the repair is sensible, fixing it may be the better option.

Replacement starts to make more sense when breakdowns become frequent, repair costs keep increasing, important parts become difficult to obtain or the boiler no longer suits the property.

If you currently have a fault, see our boiler repair service.

You can also read our guide to how long a boiler should last.

What Should a New Boiler Quote Include?

Before comparing prices, make sure the installers are actually quoting for the same work.

• Exact boiler make, model and output
• Proposed boiler position
• Flue arrangement
• Heating controls
• Magnetic system filter
• System cleaning and corrosion inhibitor
• Any pipework alterations
• Removal of the old boiler
• Commissioning and handover
• Warranty or guarantee registration
• Building Regulations notification where applicable

Check Your Gas Boiler Installer

Gas boiler work must be carried out by a suitably qualified Gas Safe registered engineer. You can check an engineer or registered business directly through the Gas Safe Register.

Let’s Heat operates under Gas Safe Registration No. 977042.

How Long Does a New Boiler Take to Install?

The time needed depends on the work involved.

A straightforward replacement in the same suitable position can normally be completed much quicker than moving the boiler or converting the heating system.

See our guide to how long it takes to fit a boiler for the common installation scenarios.

Frequently Asked Questions

Which type of boiler is best for most homes?

There is no single best boiler type for every home. A combi suits many smaller and medium-sized properties, while a system boiler with stored hot water can be more suitable where hot-water demand is higher.

Should I choose a combi or system boiler for two bathrooms?

A system boiler can make more sense where two bathrooms regularly need hot water at the same time. The household’s actual usage, incoming water supply and existing heating arrangement should still be assessed.

What size boiler do I need?

The heating output should be based on the property’s heating requirement. A combi also needs to meet the household’s hot-water demand, so bathroom use and incoming mains-water performance are important.

Is a 30kW boiler enough for a 3-bedroom house?

It may be, but bedroom count alone is not enough to choose the boiler. Heat requirement, radiators, bathrooms and, for a combi, hot-water demand should all be considered.

Is it worth replacing a 10-year-old boiler?

Not automatically. If the boiler is reliable and only requires a sensible repair, keeping it may be the better option. Frequent breakdowns, costly repairs or poor suitability for the home can make replacement more sensible.

Which boiler brand is most reliable?

Reliability depends on the individual model, installation quality, heating-system condition and maintenance as well as the manufacturer. It is better to compare suitable models rather than assume every boiler from one brand is the same.

How much does a new boiler cost?

The price depends on the boiler selected and the installation work required. A straightforward like-for-like replacement normally costs less than moving the boiler or changing the system type. See our new boiler cost guide for current Let’s Heat package prices and UK cost information.

Do I need to replace my radiators with a new boiler?

Not necessarily. Existing radiators can normally remain if they are in suitable condition and provide enough heat for the rooms. Leaks, corrosion, sludge or inadequate output should be assessed as part of the installation.

Do I need a hot-water cylinder?

A combi boiler does not normally need a separate hot-water cylinder. System and regular boilers use stored hot water, so they normally work with a cylinder.

Can I move my new boiler to another room?

Usually, provided a suitable location and compliant flue, condensate and pipework arrangement can be achieved. Moving the boiler normally increases the amount of installation work.

Choosing Your New Boiler

The main point from this new boiler guide is simple: start with the home rather than the boiler brand.

Work out which boiler type suits the property, how much hot water the household actually uses, what heating output is needed and whether the existing heating arrangement should be kept or changed.

Once those points are clear, comparing individual boiler models becomes much easier.

You can compare our new boiler options, learn more about boiler installation or get a new boiler quote.