The Navien NCB700-3S/54K is a wall-hung, room-sealed gas condensing Combi Crossover boiler rated at 54kW — the first product of its kind capable of delivering hot water to three bathrooms simultaneously. Navien's ON technology maximises recirculation of domestic hot water to combine the consistent flow of a system boiler with the space-saving convenience of a combi, eliminating the slow heat-up times and flow-rate drop-off of a conventional combi at this scale.
25.8 l/min
DHW Flow (ΔT30°C)
12 yrs
Parts & Labour Warranty
Gas Safe Registration Required
Installation, commissioning and servicing of this boiler must be carried out by a Gas Safe registered engineer. A Benchmark commissioning checklist must be completed and left with the end user, and the flue must be positioned in accordance with the clearances set out in the manufacturer's installation and operation manual.
LPG Conversion & Sizing
The boiler is shipped ready to fire on natural gas, with an LPG conversion kit included in the packaging for field conversion by a suitably qualified Gas Safe engineer. At 54kW DHW output, this is a large-property boiler — confirm mains water flow rate and pressure are sufficient to make full use of its 25.8 l/min hot water delivery before ordering.
Why This Boiler
Navien ON Recirculation Technology
Built-in DHW recirculation keeps hot water primed at outlets around the property, removing the wait and the fluctuation between hot and cold that affects conventional combi boilers under heavy simultaneous demand.
Three Showers Simultaneously
Rated to deliver hot water to three bathrooms at once, the NCB700 ON removes the need to choose between a combi's compact footprint and a system boiler's simultaneous hot water capacity.
Industry-Leading 15:1 Turndown
A 15:1 modulation ratio allows the burner to idle at a very low minimum output, improving part-load efficiency and comfort across a huge range of demand.
NaviCirc™ Hot Water Return
NaviCirc™ simplifies the setup of a hot water return system, supporting fast, consistent delivery to outlets throughout a larger home.
Hydrogen-Ready (20% Blend)
Tested and approved for use with up to a 20% hydrogen blend in the gas supply, helping future-proof the installation.
12-Year Warranty
Navien back the NCB700 ON with a 12-year parts and labour warranty as standard — the longest in the current Navien gas range.
Technical Specification
| General |
| Article number |
PNCB7000054L001 (NCB700-3S/54K) |
| Boiler type |
Wall-hung, room-sealed, fan-assisted condensing Combi Crossover |
| Fuel type |
Natural gas (LPG conversion kit included, field conversion required) |
| Dimensions (W x D x H) |
440 x 353 x 695 mm |
| Guarantee |
12 years parts and labour |
| Shower rating |
Three showers |
| Heating Performance |
| Heat input range |
3.5 – 35.0 kW |
| Heat output range (80/60°C) |
3.4 – 34.0 kW |
| Modulation (max/min) |
15:1 |
| Domestic Hot Water |
| DHW heat input range |
3.5 – 52.4 kW |
| DHW output range |
3.5 – 54.0 kW |
| DHW flow rate (ΔT = 25°C) |
31.0 l/min |
| DHW flow rate (ΔT = 30°C) |
25.8 l/min |
| DHW flow rate, kitchen tap (ΔT = 45°C) |
17.2 l/min |
| Performance & Emissions |
| ErP efficiency |
A (94%) — A+ (98%) with single Smart Plus control |
| NOx classification |
Class 6 |
| Lift weight |
46 kg |
| Flue |
| Flue diameter |
Coaxial 60/100mm |
| Max. horizontal coaxial flue length |
20 m |
| Max. vertical coaxial flue length |
21 m |
Frequently Asked Questions
What does ON technology actually do?
It maximises recirculation of domestic hot water around the property's pipework, so hot water is already primed at outlets rather than needing to travel the full length of pipe from the boiler on every draw-off — reducing water wastage and the wait for hot water.
Can this boiler really supply three bathrooms at once?
Yes — Navien designed the NCB700 ON specifically to deliver hot water to three bathrooms simultaneously without the flow or temperature drop-off typical of smaller combi boilers under similar demand.
Do I still need a hot water cylinder with this boiler?
No. As a Combi Crossover model, the NCB700 ON supplies domestic hot water directly, without needing a separate storage cylinder, despite its system-boiler-level performance.
Can I run this boiler on LPG?
An LPG conversion kit is included in the boiler's packaging as standard, but the boiler ships configured for natural gas. Conversion must be carried out by a Gas Safe registered engineer holding the appropriate LPG qualification.
Can I install this boiler myself?
No. UK law requires that all gas boiler installation, commissioning and servicing work is carried out by a Gas Safe registered engineer.
