The 5 Best System Boilers [2026]

UK landlords searching for the best system boilers need dependable, efficient models that pair with unvented cylinders to deliver reliable central heating and strong hot water flow rates in multi-bathroom rental properties, while supporting EPC improvements and minimising maintenance disruptions for tenants.

The 5 Best System Boilers: At a Glance

The leading system boilers for landlords in 2026 offer A-rated condensing efficiency to boost EPC ratings, long warranties that protect against tenant-related breakdowns, straightforward Gas Safe servicing, and robust performance for medium-to-large rented homes with existing hot water cylinders.

Model	Efficiency (ErP)	Typical Unit Cost	Installed Cost (approx.)	Warranty (accredited install)	Trustpilot Rating	Key Landlord Benefit
Worcester Bosch Greenstar 8000 Life System	94%	£1,500–£1,800	£3,100–£4,000	Up to 12 years	4.6/5	Largest UK service network
Viessmann Vitodens 100-W System	Up to 98%	£1,300–£1,600	£2,900–£3,800	Up to 12 years	4.6/5	Superior efficiency & stainless steel
Vaillant ecoTEC Plus 635 System	94%	£1,400–£1,700	£3,000–£3,900	Up to 10 years	4.5/5	Quiet operation & smart controls
Ideal Logic Max System	94%	£1,000–£1,300	£2,700–£3,500	Up to 12 years	4.8/5	Excellent value & easy maintenance
ATAG iS35 System	94%	£1,450–£1,700	£3,000–£3,900	Up to 14 years	4.6/5	Longest warranty & premium build

Notes: Prices are 2026 UK averages for 30-35kW system boilers (suitable for 3-5 bedroom rentals). Installed costs include standard Gas Safe installation, flue, and basic controls. All are wall-mounted A-rated condensing system boilers designed for unvented cylinders. Actual costs vary by property, location, and cylinder compatibility.

If you’re a landlord looking to upgrade heating in rental properties with reliable best system boilers, request a new boiler quote from Boilers 2 Go for expert advice on sizing, EPC compliance, and professional installation.

1. Worcester Bosch Greenstar 8000 Life System

The Worcester Bosch Greenstar 8000 Life System ranks highly among the best system boilers for landlords due to its proven reliability and unmatched nationwide engineer support in tenanted properties.

Specifications and Features

• 30-35kW output for larger rentals (15-20+ radiators)
• Full-colour touchscreen diagnostics
• Pre-plumbing jig option for faster replacement
• Smart thermostat compatible
• Built-in system filter protection

Efficiency

94% ErP A-rated condensing performance for strong EPC gains.

Estimated Cost of the Boiler Unit

£1,500–£1,800.

Costs with Installation

£3,100–£4,000.

Running Costs

Precise modulation reduces gas consumption and tenant bills.

Which? Trustpilot Ratings

4.6/5 Trustpilot; frequent Which? Best Buy winner.

2. Viessmann Vitodens 100-W System

The Viessmann Vitodens 100-W System excels among the best system boilers for its top-tier efficiency and corrosion-resistant components, ideal for future-proofing rental investments.

Specifications and Features

• 25-35kW outputs
• Inox-Radial stainless steel heat exchanger
• Lambda Pro Plus combustion control
• Compact design
• Hydrogen blend ready (20%)

Efficiency

Up to 98% seasonal efficiency.

Estimated Cost of the Boiler Unit

£1,300–£1,600.

Costs with Installation

£2,900–£3,800.

Running Costs

Excellent modulation delivers significant long-term savings.

Which? Trustpilot Ratings

4.6/5 Trustpilot; Which? Recommended.

3. Vaillant ecoTEC Plus 635 System

The Vaillant ecoTEC Plus 635 System is a strong contender in the best system boilers range for its quiet running and advanced controls that enhance tenant satisfaction in rentals.

Specifications and Features

• 35kW output
• IoniDetect for cleaner combustion
• vSMART app compatibility
• Built-in pump and expansion vessel
• Frost protection

Efficiency

94% ErP A-rated.

Estimated Cost of the Boiler Unit

£1,400–£1,700.

Costs with Installation

£3,000–£3,900.

Running Costs

Low cycling reduces fuel waste.

Which? Trustpilot Ratings

4.5/5 Trustpilot; Which? recommended.

4. Ideal Logic Max System

The Ideal Logic Max System delivers outstanding value among the best system boilers, making it popular for budget-conscious landlords seeking reliable performance in rentals.

Specifications and Features

• 30kW output suitable for most family rentals
• Front-access servicing
• Built-in filter
• Clear diagnostic display
• OpenTherm ready

Efficiency

94% ErP A-rated.

Estimated Cost of the Boiler Unit

£1,000–£1,300.

Costs with Installation

£2,700–£3,500.

Running Costs

Cost-effective with good modulation.

Which? Trustpilot Ratings

4.8/5 Trustpilot; highly praised for value.

5. ATAG iS35 System

The ATAG iS35 System offers premium longevity among the best system boilers with one of the longest warranties, protecting landlords’ investments over many tenancies.

Specifications and Features

• 35kW output
• Stainless steel heat exchanger
• Lifetime heat exchanger guarantee option
• Compact footprint
• Smart control compatible

Efficiency

94% ErP A-rated.

Estimated Cost of the Boiler Unit

£1,450–£1,700.

Costs with Installation

£3,000–£3,900.

Running Costs

High build quality minimises repairs.

Which? Trustpilot Ratings

4.6/5 Trustpilot.

How to choose the Best system boilers

Choosing the best system boilers for landlords rental properties involves weighing warranty length, service network availability, efficiency for EPC compliance, cylinder compatibility, and ease of maintenance to reduce void periods and tenant complaints.

Choose the Worcester Bosch Greenstar 8000 Life System if you need the strongest nationwide Gas Safe support for multiple rental properties.

Don’t choose Worcester Bosch if upfront costs are your biggest constraint.

Choose the Viessmann Vitodens 100-W System if maximum efficiency and hydrogen readiness are priorities for meeting future EPC standards.

Don’t choose Viessmann if local engineer familiarity is limited.

Choose the Vaillant ecoTEC Plus 635 System if quiet performance and smart controls will improve tenant experience.

Don’t choose Vaillant if the longest warranty is more important than noise levels.

Choose the Ideal Logic Max System if you want great value and straightforward servicing.

Don’t choose Ideal if premium features like advanced diagnostics are essential.

Choose the ATAG iS35 System if extended warranty protection is your top priority for long-term rental ownership.

Don’t choose ATAG if parts availability in your area is restricted.

Looking for a New Boiler Quote?

Installing one of the best system boilers in your rental properties ensures reliable heating, better EPC ratings, fewer repairs, and improved tenant comfort. Request a new boiler quote from Boilers 2 Go today for competitive pricing, expert landlord guidance, and accredited Gas Safe installation tailored to the private rented sector.

FAQs

What makes system boilers preferable for HMOs or properties with multiple bathrooms?

System boilers maintain consistent hot water pressure from a stored cylinder, avoiding flow rate drops when several outlets are used simultaneously.

How do system boilers compare to heat pumps for landlord EPC compliance in 2026?

While heat pumps offer higher potential ratings, modern high-efficiency system boilers paired with good insulation and controls can still achieve EPC C reliably and at lower upfront cost.

Are there specific legal requirements for system boilers in rented properties?

Landlords must ensure annual Gas Safe safety checks, keep service records available for tenants, and maintain the boiler to prevent carbon monoxide risks.

Can landlords claim tax relief or grants on system boiler replacements?

Energy efficiency upgrades including system boilers may qualify as deductible revenue expenses or benefit from schemes like the Boiler Upgrade Scheme (mainly for heat pumps) and local authority grants.

What cylinder size is typically recommended to pair with a 30-35kW system boiler in rentals?

A 210-300 litre unvented cylinder is common for family rentals, providing ample stored hot water without excessive standing heat loss.