Choosing the Right Boiler for Your Home
If your boiler needs replacing — or you're moving into a new property and rethinking the heating — one of the most important decisions is choosing the right type of boiler. In the UK, there are three main types: combi, system, and regular (also called conventional or heat-only). Each has distinct advantages and drawbacks, and the best choice depends on your property size, hot water demand, and existing pipework.
As London's leading boiler installation specialists, we fit all three types regularly. Here's our honest, jargon-free guide to help you decide which is right for your home.
Combi Boilers
How They Work
A combination (combi) boiler provides both central heating and hot water on demand from a single, compact unit. There's no need for a separate hot water cylinder or cold water storage tank — the boiler heats water directly from the mains when you open a hot tap or turn on the heating.
Advantages
- Compact size: No cylinder or tank required, freeing up space in airing cupboards and lofts. Ideal for London flats and smaller properties.
- Instant hot water: Unlimited hot water on demand (though flow rate is limited — see disadvantages).
- Easy to install: Fewer components and less pipework mean faster, cheaper installation.
- Energy efficient: No heat loss from a stored cylinder of hot water.
- Lower installation cost: Typically the cheapest of the three types to install.
Disadvantages
- Limited hot water flow rate: A combi can typically supply one shower or bath at a time. If someone opens a second hot tap, both will experience reduced flow and temperature. This is the biggest limitation for larger households.
- Dependent on mains pressure: If your mains water pressure is low (common in some older London buildings), a combi may not deliver adequate performance.
- Not ideal for large homes: Properties with 3+ bathrooms typically need more hot water capacity than a combi can deliver.
Best For
Flats, studios, 1-2 bedroom houses, and any property where space is at a premium. Perfect for couples and small families who rarely need hot water from multiple outlets simultaneously.
Popular Models
Worcester Bosch Greenstar 4000, Vaillant ecoTEC Plus, Ideal Vogue Max Combi, Baxi 800 Combi.
System Boilers
How They Work
A system boiler works with a hot water cylinder (usually in an airing cupboard) but doesn't require a cold water storage tank in the loft. The boiler heats water and stores it in the cylinder, ready for use. The system components — pump, expansion vessel, and controls — are built into the boiler, making installation simpler than a regular boiler.
Advantages
- Strong hot water flow to multiple outlets: Because hot water is stored in a cylinder, multiple taps and showers can run simultaneously without losing pressure or temperature.
- Compatible with solar thermal: The cylinder can be heated by solar panels as well as the boiler, reducing gas bills.
- No loft tank required: Unlike regular boilers, there's no need for a cold water storage tank in the loft.
- Good water pressure: Supplied at mains pressure (with an unvented cylinder), delivering a powerful shower without needing a separate pump.
Disadvantages
- Requires space for a cylinder: You need an airing cupboard or utility area to house the hot water cylinder.
- Hot water isn't instant: Once the stored hot water is used up, you need to wait for the cylinder to reheat (typically 20–40 minutes depending on size).
- Higher installation cost than a combi: The cylinder and additional pipework add to the overall cost.
Best For
Medium to large homes (3+ bedrooms) with 2 or more bathrooms and higher hot water demand. Families who regularly run multiple showers, baths, or taps at the same time.
Popular Models
Worcester Bosch Greenstar 8000 Life System, Vaillant ecoTEC Plus System, Ideal Vogue Max System.
Regular (Conventional / Heat-Only) Boilers
How They Work
A regular boiler works with both a hot water cylinder and a cold water storage tank (typically in the loft) plus a feed and expansion tank. This is the oldest and most traditional type of boiler system in the UK. The cold water tank feeds the heating system by gravity, and the boiler heats water that's stored in the cylinder.
Advantages
- Suits existing systems: If your property already has a traditional heating system with tanks and a cylinder, a regular boiler is often the simplest and most cost-effective replacement.
- High hot water output: A large cylinder can supply multiple bathrooms simultaneously.
- Compatible with older radiator systems: Some older heating systems with open-vented pipework can only work with a regular boiler.
- Reliable technology: Simple, proven design with fewer electronic components.
Disadvantages
- Requires the most space: You need room for a cylinder, a cold water tank in the loft, and a feed/expansion tank.
- Lower water pressure (gravity-fed): Unless you add a pump, hot water pressure is lower than mains-fed systems.
- More complex installation: More components and pipework than combi or system boilers.
- Energy loss from stored water: The cylinder and tanks lose heat over time, reducing overall efficiency.
Best For
Larger and older properties that already have the pipework for a regular system. Properties where converting to a combi or system boiler would require extensive (and costly) pipework changes.
Popular Models
Worcester Bosch Greenstar 4000 Regular, Vaillant ecoTEC Plus Regular, Ideal Vogue Max Regular.
Quick Comparison
- Best for small flats/1-2 bed: Combi boiler
- Best for 3+ bed family home: System boiler
- Best for older/larger homes with existing tanks: Regular boiler
- Best for multiple bathrooms: System or regular boiler
- Cheapest to install: Combi boiler
- Best water pressure: System boiler (with unvented cylinder)
- Most space-saving: Combi boiler
London-Specific Considerations
London properties have some unique characteristics that affect boiler choice:
- Small flats and conversions: Space is at a premium in London, making combi boilers the most popular choice for flats, studios, and 1-2 bedroom conversions. No cylinder or tanks means more usable space.
- Victorian and Edwardian terraces: Many of these properties have existing regular boiler systems with tanks in the loft. Depending on the property and budget, you can either replace like-for-like or convert to a system boiler (removing the loft tanks).
- New builds and modern apartments: Typically designed for combi boilers or, in developments with communal heating, heat interface units (HIUs).
- Mains water pressure: Some older areas of London have lower mains pressure. If mains pressure is below 1.0 bar, a combi may struggle. Your installer should check this before recommending a boiler type.
How Much Does Each Type Cost to Install?
Typical installation costs in London (including the boiler, labour, and standard fittings):
- Combi boiler: £1,950–£3,500 (like-for-like replacement). £2,500–£4,500 if converting from a regular or system boiler.
- System boiler: £2,500–£4,500 (including cylinder).
- Regular boiler: £2,200–£4,000 (like-for-like replacement).
For a detailed breakdown, see our London boiler pricing guide. We also offer 0% finance to help spread the cost.
Get Expert Advice
Choosing the right boiler type isn't always straightforward, and the wrong choice can lead to performance issues, wasted money, or unnecessary disruption. Our engineers will visit your property, assess your heating demands, check your mains pressure, and recommend the best solution for your specific situation — with no obligation to proceed.
Book a free survey or call us on 020 7622 0444. We install Worcester Bosch, Vaillant, Ideal, and Baxi boilers across all London boroughs, with manufacturer warranties of up to 12 years.