The Baxi 600 System 2 is a wall-hung condensing gas system boiler available in three outputs — 15 kW (615), 18 kW (618), and 24 kW (624) — making it an outstanding choice whenever you need plentiful, simultaneous hot water across multiple bathrooms. Built around a stainless steel heat exchanger, it achieves an ErP A-rating and 93% seasonal efficiency, cutting running costs while reducing your carbon footprint. A seven-year parts and labour warranty (when registered within 30 days) and compatibility with Baxi uSense smart controls complete a boiler that balances everyday practicality with long-term reliability.
7 Year
Parts & Labour Warranty
H₂-Ready
Up to 20% Hydrogen Blend
Gas Safe Registration Required — Installation, commissioning, LPG conversion, and all maintenance work must be carried out by a Gas Safe registered engineer in accordance with current Building Regulations and the Benchmark Commissioning Checklist.
System Boiler — Cylinder Required — The Baxi 600 System 2 heats the central heating circuit directly and works with a compatible unvented or vented hot water cylinder (such as the Baxi or Megaflo Eco range) to deliver stored mains-pressure hot water to multiple outlets simultaneously.
Choosing the Right Output — The 615 (15 kW) suits smaller homes with up to 10 radiators and a single bathroom. The 618 (18 kW) is ideal for medium homes with one or two bathrooms, and the 624 (24 kW) is recommended for larger homes or properties with multiple bathrooms and higher heat demands. All three outputs share identical dimensions and installation footprint.
Stainless Steel Heat Exchanger
The stainless steel heat exchanger offers superior resistance to corrosion and scale compared to aluminium alternatives, contributing to the boiler's long service life and consistent thermal performance across all three output sizes.
93% Seasonal Efficiency — ErP A-Rated
All three models achieve 93% seasonal efficiency and hold an ErP A-rating for central heating, meeting the EU Energy-related Products Directive standards and helping to keep annual gas bills meaningfully lower than older non-condensing boilers.
Pre-Heated Siphonic Condensate Trap
The pre-heated siphonic condensate trap warms condensate before it exits the boiler, discharging it all at once rather than in small trickles. This significantly reduces the risk of frozen condensate pipes in cold weather, avoiding winter shutdowns and costly callouts.
Natural Gas & LPG Compatible
All models can be manually converted between natural gas (G20) and LPG (G31) without purchasing an additional accessory kit. The conversion is carried out by a Gas Safe engineer via the boiler's gas valve settings, making it cost-effective for off-grid properties.
EasyFill Permanent Filling Link
The built-in EasyFill permanent filling link lets the homeowner top up system pressure without needing to attach a temporary hose or call an engineer, simplifying routine maintenance and helping maintain optimum boiler performance between services.
Smart Control Ready — OpenTherm & uSense
The 600 System 2 supports OpenTherm modulating control, allowing compatible thermostats such as Nest and Hive to vary boiler output rather than simply switching it on and off. The optional Baxi uSense Wi-Fi thermostat adds smartphone scheduling and remote control capability.
Compact & Cupboard-Friendly
At just 700 mm high × 390 mm wide × 285 mm deep and weighing only 28 kg, the 600 System 2 is designed to fit neatly inside a standard 290 mm-deep kitchen or utility cupboard, keeping hallways and living spaces clutter-free.
Hydrogen-Blend Ready
The boiler is certified for use with natural gas containing up to 20% hydrogen (H₂), ensuring it is prepared for the UK government's planned transition to low-carbon hydrogen-blended gas networks without requiring hardware upgrades.
7-Year Parts & Labour Warranty
Register within 30 days of installation, complete the Benchmark Commissioning Checklist, and ensure the boiler receives an annual service to maintain the full 7-year parts and labour warranty — one of the longer manufacturer-backed guarantees in this product category.
Technical Specifications
| Specification |
615 System 2 |
618 System 2 |
624 System 2 |
| Baxi Part Number (MPN) |
7798687 |
7802020 |
7802241 |
| Gas Council Number |
41-884-01 |
41-884-02 |
41-484-03 |
| Heat Output (kW) |
15 kW |
18 kW |
24 kW |
| Boiler Type |
Wall-hung condensing gas system boiler |
| Seasonal Efficiency |
93% |
| ErP Energy Rating |
A (Central Heating) |
| Heat Exchanger Material |
Stainless steel |
| Gas Type |
Natural Gas (G20) / LPG (G31) — manual conversion, no kit required |
| Hydrogen Compatibility |
Suitable for up to 20% H₂ blend |
| CH Flow Temperature Range |
25 – 80 °C (adjustable) |
| Max System Pressure |
3 bar |
| Electrical Supply |
230 V / 50 Hz / single phase |
| Dimensions (H × W × D) |
700 × 390 × 285 mm |
| Weight |
28 kg |
| Minimum Cupboard Depth |
290 mm |
| Condensate Trap |
Pre-heated siphonic (anti-freeze) |
| Filling System |
EasyFill permanent filling link |
| Controls Compatibility |
OpenTherm; Baxi uSense (optional); Nest, Hive & other OT thermostats |
| Cylinder Compatibility |
Baxi cylinders; Megaflo Eco range |
| Warranty |
7 years parts & labour (registration required within 30 days) |
Frequently Asked Questions
What is the difference between the 615, 618, and 624 System 2 models?
The only functional difference between the three models is their maximum heat output: the 615 delivers 15 kW, the 618 delivers 18 kW, and the 624 delivers 24 kW. All three share identical dimensions (700 × 390 × 285 mm), weight (28 kg), seasonal efficiency (93%), ErP A-rating, warranty terms, and feature set. The correct output for your home depends on the number of radiators and bathrooms — your Gas Safe installer can carry out a heat loss calculation to advise you.
Does the Baxi 600 System 2 need a hot water cylinder?
Yes. As a system boiler, the 600 System 2 heats your central heating circuit directly but requires a separate unvented or vented hot water cylinder to store and deliver domestic hot water. It is compatible with Baxi cylinders and the Megaflo Eco range. The advantage over a combi boiler is that the cylinder allows multiple taps and showers to run simultaneously at mains pressure, making it the preferred choice for homes with two or more bathrooms.
Can the Baxi 600 System 2 run on LPG?
Yes. All three models can be manually converted between natural gas (G20) and LPG (G31) without purchasing a separate conversion kit. The conversion is performed by a Gas Safe registered engineer via the boiler's gas valve adjustment procedure. This makes the 600 System 2 a cost-effective option for properties that are not connected to the mains gas grid.
What smart thermostats are compatible with the Baxi 600 System 2?
The 600 System 2 supports OpenTherm (OT) modulating communication, which allows it to work with popular smart thermostats including Nest, Hive, and other OpenTherm-compatible devices. With OpenTherm, the thermostat and boiler communicate continuously, enabling the boiler to modulate its output rather than simply cycling on and off, which improves efficiency. Baxi also offer the uSense Wi-Fi thermostat as an optional add-on for smartphone-based scheduling and remote control.
How do I activate the 7-year warranty on the Baxi 600 System 2?
To maintain the full 7-year parts and labour warranty, three conditions must all be met: (1) the installer must complete the Benchmark Commissioning Checklist at the time of installation; (2) the boiler must be registered at baxi.co.uk/registration within 30 days of installation; and (3) the boiler must receive an annual service from a qualified engineer. Failure to meet any of these conditions may void the warranty — please refer to the full terms at baxi.co.uk/terms.
Is the Baxi 600 System 2 hydrogen-blend ready?
Yes. The 600 System 2 is certified to operate on natural gas containing up to 20% hydrogen (H₂) by volume, in line with emerging UK gas network decarbonisation plans. No hardware modifications are required for hydrogen-blended gas at this level. This future-proofing means the boiler will remain compliant if and when hydrogen blending is introduced to the UK grid.
