What is the cheapest type of boiler to install?

Combi boilers are the cheapest to buy and install, ranging from £1,500–£3,500 for the unit plus £500–£1,500 for installation. They don’t need a cylinder or tank, reducing total cost significantly.

Should I switch from a regular boiler to a combi?

For small to medium homes with one bathroom, switching to a combi can save space and reduce energy bills. However, the conversion costs £3,000–£5,500 due to pipework changes. For larger homes with multiple bathrooms, keeping a system boiler is usually better.

Last verified April 2026

Combi vs System vs Regular Boiler Costs

The three main types of boiler in the UK serve different needs. Your choice affects both the upfront cost and long-term running expenses. Here's a detailed comparison to help you decide.

Combi Boiler

70% of UK installations

£1,500–£3,500

supply only · avg £2,300

Heats water on demand directly from the mains. No separate hot water cylinder or cold water tank needed. Most popular choice in the UK.

Best for:

Small to medium homes (1-3 bedrooms) with one bathroom

Advantages

Compact size
Instant hot water
No tank needed
Lower installation cost
Easy to maintain

Disadvantages

Struggles with multiple taps at once
Not ideal for large homes
Depends on mains pressure

Installation cost: £500–£1500 on top of unit price

System Boiler

20% of UK installations

£2,000–£4,000

supply only · avg £2,800

Works with a hot water cylinder but doesn't need a cold water tank in the loft. Good balance of capacity and simplicity.

Best for:

Medium to large homes (3-5 bedrooms) with multiple bathrooms

Advantages

Good water pressure to multiple taps
Compatible with solar thermal
No loft tank
Reliable for larger homes

Disadvantages

Needs space for hot water cylinder
Hot water can run out
Higher installation cost than combi

Installation cost: £800–£2000 on top of unit price

Regular (Conventional) Boiler

10% of UK installations

£1,800–£3,800

supply only · avg £2,500

Also called a heat-only boiler. Requires both a hot water cylinder and a cold water tank in the loft. Traditional system found in older UK homes.

Best for:

Large homes with existing traditional heating systems and multiple bathrooms

Advantages

Works with existing pipework
Excellent for high-demand homes
Compatible with solar thermal
Good water flow to multiple outlets

Disadvantages

Needs most space
Requires loft tank
More complex installation
Higher total cost

Installation cost: £1000–£2500 on top of unit price

Side-by-Side Comparison

Feature	Combi	System	Regular
Unit cost	£1,500–£3,500	£2,000–£4,000	£1,800–£3,800
Install cost	£500–£1,500	£800–£2,000	£1,000–£2,500
Hot water cylinder	Not needed	Required	Required
Loft tank	Not needed	Not needed	Required
Multiple bathrooms	Struggles	Good	Excellent
Space required	Minimal	Moderate	Most
Solar compatible	Limited	Yes	Yes

Not sure which type you need?

Check our cost-by-house-size guide for specific recommendations based on your property.

Cost by House Size