Combination Boiler Guide
All-in-one boiler providing heating and hot water on demand without the need for separate tanks or cylinders.
UK Market Share
55%
Avg Efficiency
92%
Price Range
£600 - £2,000
Typical Warranty
10yr
What Does a Combination Boiler Look Like?
Typical combination boiler installation in a UK home
How Combination Boilers Work
Overview
Combination boilers are the most popular type in the UK, combining a water heater and central heating boiler in one compact unit. They heat water directly from the mains when you turn on a tap, meaning you get hot water instantly without the need for a storage cylinder or cold water tank.
The Process:
When you turn on a hot tap, cold water flows into the boiler where it is rapidly heated by the gas burner or heating element. The hot water then flows directly to your tap. For central heating, the boiler heats water which is pumped through your radiators before returning to the boiler to be reheated.
System Diagram
Complete system layout showing water flow and heating distribution
Combination Boiler Pros and Cons
Advantages
Space-saving design
No need for separate hot water cylinder or cold water tank, freeing up valuable cupboard space.
Instant hot water
Hot water is heated on demand, so you never run out and don't waste energy heating a tank.
Lower installation costs
Simpler installation with fewer components means lower upfront costs.
Energy efficient
Only heats water when needed, reducing energy waste.
Good water pressure
Water comes directly from the mains, providing strong pressure.
Cheaper to run
No heat loss from storing hot water, making running costs lower.
How Combination Boilers compare to other types
Disadvantages
Limited hot water flow rate
Water flow reduces if multiple taps are used simultaneously.
Not ideal for multiple bathrooms
Struggles to supply enough hot water when demand is high.
Performance depends on mains pressure
Poor water pressure will result in weak flow from taps.
No backup hot water
If boiler breaks down, you have no heating or hot water.
Temperature can fluctuate
Water temperature may vary when multiple outlets are used.
Is a Combination Boiler Right for Your Home?
Suitability Overview
✓ Best suited for:
Small to medium homes (1-3 bedrooms) with 1-2 bathrooms, flats, properties with limited space, homes with good mains water pressure
✗ Not suitable for:
Large homes with multiple bathrooms being used simultaneously, properties with poor mains water pressure, homes with very high hot water demand
Ideal property types
Detailed Suitability by Property Type
| Property | Beds | Baths | Score | Recommendation |
|---|---|---|---|---|
| Flat | 1 | 1 | 10/10 | Excellent Perfect for flats - compact, efficient, no space wasted on tanks |
| Terraced House | 2 | 1 | 9/10 | Excellent Ideal for 2-bed terraced houses with one bathroom |
| Terraced House | 3 | 1 | 8/10 | Good Works well for 3-bed houses with one bathroom |
| Semi-Detached | 3 | 1 | 8/10 | Good Suitable for semi-detached with one bathroom |
| Semi-Detached | 3 | 2 | 5/10 | Fair Can work but pressure may drop with simultaneous use |
| Detached House | 4 | 2 | 4/10 | Poor Struggles with multiple bathrooms simultaneously |
| Detached House | 5 | 3 | 2/10 | Not Recommended Insufficient for large detached house with multiple bathrooms |
Space Requirements & Installation
Components You'll Need Space For
Boiler unit
RequiredSize: 700mm H x 400mm W x 300mm D
Location: Kitchen wall or utility room
Typical Installation
Professional installation takes 1-2 days depending on your existing system
Annual Running Costs
What You'll Pay Each Year
Small (1-2 bed)
£950
per year (estimated)
Medium (3-4 bed)
£1375
per year (estimated)
Large (4+ bed)
£1800
per year (estimated)
💡 Tip: Running costs vary based on your heating usage, insulation quality, and local energy prices. These figures are UK averages based on typical usage patterns.
Popular Combination Boiler Models
| Manufacturer | Model | Output | Efficiency | Price | Warranty |
|---|---|---|---|---|---|
| Worcester Bosch | Greenstar 2000 | 30 kW | 94%A-rated | £1,200 | 10 years |
| Vaillant | ecoTEC Plus | 30 kW | 94%A-rated | £1,400 | 10 years |
| Baxi | 800 Combi | 30 kW | 93% | £950 | 7 years |
| Ideal | Logic Max Combi | 30 kW | 94%A-rated | £900 | 10 years |
| Viessmann | Vitodens 050-W | 30 kW | 94%A-rated | £1,500 | 10 years |
Prices shown are for the boiler unit only. Installation costs typically range from £500 - £1,500. Get free quotes from local installers for accurate pricing.
Frequently Asked Questions
How long does a combi boiler last?
A well-maintained combi boiler typically lasts 10-15 years. Regular annual servicing can help extend its lifespan. Modern boilers with good warranties may last even longer.
Can a combi boiler run a bath and shower at the same time?
This depends on the boiler's flow rate. Most combi boilers struggle to supply two outlets at full pressure simultaneously. For multiple bathrooms, a system boiler is usually better.
What size combi boiler do I need?
For a 2-3 bedroom house with 1 bathroom, a 28-30kW boiler is usually sufficient. Larger homes with multiple bathrooms should consider 35kW or higher, or switch to a system boiler.
Are combi boilers expensive to run?
Combi boilers are generally the cheapest type to run because they only heat water when needed, with no heat loss from stored water. Annual running costs for an average home are £800-£1,200.
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