Navien Boilers UK — Gas Combi, System & Oil Boilers with LPG Conversion

Navien Boilers — South Korea's Heating Giant, Now Available at AIZO Quality Heating

Navien is one of the world's largest boiler manufacturers, producing over 6 million units a year from its advanced manufacturing plants in South Korea. The company has built its reputation on stainless steel heat exchanger technology — the same corrosion-resistant material used in marine and industrial applications — which delivers longer service life and higher efficiency than traditional copper equivalents. Every Navien gas boiler sold through AIZO Quality Heating is ErP A-rated and engineered to deliver up to 97.5% gross seasonal efficiency.

What sets Navien apart from the established European brands is the combination of build quality, warranty length, and value. The NCB700 ON range, for example, carries a 12-year parts and labour warranty — one of the longest in the UK market — while the NCB300 offers a 10-year warranty at price points that undercut comparable models from Worcester Bosch, Vaillant, and Viessmann.

LPG-Ready Straight Out of the Box

One of the most compelling features of the Navien gas combi boiler range is that every unit ships with the LPG (liquefied petroleum gas) conversion kit included as standard. There is no separate kit to order, no extra cost, and no waiting for parts — the installer simply fits the LPG jets and adjusts the gas valve settings during commissioning. This makes Navien an exceptionally practical choice for properties that rely on bottled or bulk-tank LPG rather than mains natural gas.

Navien NCB300 — Gas Combi Boilers

The NCB300 is Navien's core combi boiler range, available in 28kW and 37kW outputs. Both models feature a stainless steel heat exchanger, built-in frost protection, a low-NOx pre-mix burner, and the LPG conversion kit in the box. The NCB300 suits 1 to 4 bedroom properties and delivers hot water at mains pressure with no need for a separate cylinder or water tank. All NCB300 models carry a 10-year parts and labour warranty when installed by an accredited Navien installer.

Navien NCB700 ON — Premium Gas Combi Boiler

The NCB700 ON is Navien's flagship combi boiler, delivering 54kW of output — enough to supply three bathrooms simultaneously with strong hot water flow. It features the same stainless steel heat exchanger technology as the NCB300 but with a more powerful burner, larger plate-to-plate heat exchanger for domestic hot water, and an extended 12-year parts and labour warranty. The LPG conversion kit is included as standard, and the boiler is OpenTherm compatible for modulating control with smart thermostats.

Navien NCB500 — Gas System Boilers

For larger homes with multiple bathrooms or higher hot water demand, the NCB500 system boiler range is the answer. Unlike a combi boiler, a system boiler works alongside a separate hot water cylinder — typically a 150–300 litre unvented cylinder — to store pre-heated water ready for use. This means you can run multiple showers, baths, and taps at the same time without any drop in pressure or temperature. The NCB500 is available in 15kW and 18kW outputs and features the same stainless steel heat exchanger build quality as the combi range.

Navien LCB700 — Blue Flame Oil Boilers

For properties that rely on oil heating — common across rural Wales, Scotland, East Anglia, and the West Country — the Navien LCB700 Blue Flame range offers a modern alternative to traditional pressure-jet oil boilers. Blue Flame technology burns kerosene in a cleaner, more controlled way, producing lower emissions and quieter operation. The range includes both internal and external models, and covers combi and system configurations, so there is a solution for virtually any oil-heated property.

Navien Boiler Comparison

Navien 60/100 Flue Components

All Navien gas boilers use a 60/100mm concentric flue system — a pipe-within-a-pipe design where the inner 60mm pipe carries combustion exhaust gases out and the outer 100mm pipe draws fresh air in. This sealed combustion system is both safe and efficient, and the 60/100 diameter is a widely used standard across the industry. AIZO Quality Heating stocks the full range of Navien-compatible flue components for horizontal, vertical, and angled flue runs.

For a standard horizontal flue run through an external wall, the 1000mm Horizontal Flue Kit is all that is needed. For installations where the boiler is positioned further from the wall, or where the flue must navigate around obstacles, the 500mm extension and 45-degree or 90-degree bends allow flexible routing. Vertical flue runs — exiting through the roof — require the Vertical Roof Terminal Kit and, on pitched roofs, the Weather Slate to provide a weatherproof seal around the pipe penetration.

How do I know which flue components I need?

Your Gas Safe registered installer will survey the boiler location and determine the flue route during the site visit. The standard horizontal kit covers most straightforward installations. If the boiler sits on an internal wall with no direct route to an external wall, your installer may need one or more bends and extensions. For vertical flue exits (through the ceiling and roof), the vertical terminal kit and weather slate are required. All Navien 60/100 flue components are compatible with the NCB300, NCB500, and NCB700 ranges.

What are the maximum flue lengths?

Maximum permissible flue lengths depend on the specific boiler model and the number of bends in the flue run. Each 90-degree bend typically reduces the maximum allowable straight run by approximately 1 metre, and each 45-degree bend reduces it by approximately 0.5 metres. Consult the boiler installation manual or contact AIZO Quality Heating for model-specific guidance.

Recommended Thermostats for Navien Boilers

A good thermostat transforms how efficiently your boiler runs. A basic on/off thermostat cycles the boiler at full power — on, off, on, off — which wastes energy and creates temperature swings. A programmable or smart thermostat lets you schedule heating around your daily routine, and models with OpenTherm compatibility allow the boiler to modulate its output smoothly rather than cycling, which can improve efficiency by 5–15%. Here are two excellent options available at AIZO Quality Heating that pair well with any Navien boiler installation.

Frequently Asked Questions

Are Navien boilers any good?

Navien is one of the world's largest boiler manufacturers, producing over 6 million units per year. Their UK range uses stainless steel heat exchangers for longer life, achieves up to 97.5% seasonal efficiency, and carries warranties of up to 12 years. The brand is well-established in North America and Asia, and has been growing rapidly in the UK market since entering it with a competitively priced range that matches or exceeds European rivals on specification.

Can I use a Navien boiler with LPG in a shepherd hut?

Yes. Every Navien NCB300 and NCB700 gas combi boiler ships with the LPG conversion kit included in the box at no additional cost. For a shepherd hut, the NCB300 28kW is the most suitable model — compact enough for a small space, powerful enough for both heating and hot water, and easily connected to a standard 47kg propane bottle or bulk LPG tank. A Gas Safe registered installer must carry out the installation and LPG conversion.

What is the difference between a combi boiler and a system boiler?

A combi boiler (NCB300, NCB700) provides both central heating and instant hot water from a single unit — no separate cylinder or water tank is needed. A system boiler (NCB500) heats the central heating circuit and works with a separate hot water cylinder to store pre-heated water. System boilers are better for homes with multiple bathrooms where hot water is used simultaneously, as the cylinder delivers stored hot water at full flow to several outlets at once.

Do Navien oil boilers work differently from gas models?

The Navien LCB700 oil boilers use Blue Flame technology, which burns kerosene in a controlled blue flame rather than a traditional yellow pressure-jet flame. This produces cleaner combustion, lower emissions, and noticeably quieter operation. The oil range is available in both internal (wall-mounted) and external (outdoor-rated) configurations, and in both combi and system variants. Oil boilers do not have LPG capability — they run exclusively on kerosene (28-second heating oil).

Which Navien boiler do I need for my property?

1–3 bed, 1 bathroom: NCB300 28kW combi — the most popular choice. Compact, efficient, and LPG-ready.

3–4 bed, 1–2 bathrooms: NCB300 37kW combi — higher hot water flow rate for larger properties or homes with two shower points.

4+ bed, 2–3 bathrooms: NCB700 ON 54kW combi — the premium choice for large homes with simultaneous hot water demand.

Large homes with 3+ bathrooms: NCB500 15kW or 18kW system boiler paired with a 200–300L unvented cylinder — best for maximum hot water storage and flow.

Off-grid oil-heated properties: LCB700 Blue Flame range — choose combi or system, internal or external, based on your property layout and hot water needs.