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Navien NCB ON Gas Combi Boiler Review

Viessmann Vitodens 050-W Gas/LPG Boiler | Boilerhut
Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: January 15, 2024. Updated: May 17, 2024

Boiler only price: from £1,614

(Boiler-only price: comparing five or more suppliers, including Screwfix and Plumbase. Correct May 2024).

The Navien Condensing NCB ON gas combi boilers are versatile and can be installed on a wall anywhere in your home. Manufactured from steel and brass components and with easy-to-use controls, they provide reliability and high efficiency.

The NCB ON range includes the 500 and 700 models, which range in power outputs from 32kW up to 54kW. This review doesn’t look at the NCB300 as it is not their new ‘ON’ variant.


The Navien NCB ON range is their latest gas combi boiler. They offer great heating and hot water flexibility and high efficiency. The NCB500 version is great for medium-sized homes, being able to power two showers and a tap. Whilst the NCB700 can manage three showers in larger homes.

Both models are similar but the NCB700 is larger, heavier and more powerful. It is their flagship gas boiler and comes with a 12-year warranty, two more than the NCB500. The 54kW model modulates at 1:15, enabling it to save you even more money on your heating bill.

Key Features

The NCB500 and 700 ON is compatible with all the latest smart heating controls, including Tado, Hive and Nest.

  • Due to the size and weight, it can be installed anywhere. The NCB500 ON is smaller and can fit in more places. The NCB700 is larger as it is more powerful.
  • Includes a control panel for access to the boiler as well as troubleshooting management.
  • Integrates with smart technology, including the prominent names in the market.
  • Energy efficient with an ErP ‘A’ rating.
  • The NCB500 OB has a 10-year warranty and the NCB700 ON has a 12-year warranty.
  • Up to 22 litres.minute hot water flow rate – three showers at once.
  • Stainless steel heat exchangers.

Technical Specification

Manufacturer Navien
Model NCB500 ON NCB700 ON
Condensing Yes
Efficiency Rating 93% 94%
Energy Efficiency Class A Rated
LPG Compatible Yes – with included kit
Warranty Up to 10 years Up to 12 years
Central Heating Max. Output 26kW 35kW
Modulation 1:10 1:15
Hot Water Flow Rate (45°C temp. rise) up to 13.1 litres/minute up to 17.2 litres/minute
Mounting Wall mounted 
Weight 34kg 46kg
Dimensions (HxWxD) mm 680 x 395 x 285 695 x 440 x 335
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Our thoughts

The Navien NCB range is easy to install and offers a generous warranty period. It is also low polluting due to its high energy efficiency rating and is easy to control via the intuitive control panel display.

The two models span 5 power outputs for great flexibility. These boilers can generally provide adequate hot water for most average-sized family homes. But beware, like all boilers, it may be restricted by the incoming cold water feed flow rate. It will never be able to heat more water than is coming in.

The latest technology

You can use the Navien NCB via the conventional programmable control panel or thermostat. But the options don’t stop there. You can upgrade to a smart energy system, which can improve the energy efficiency of the boiler even further. This model is compatible with smart thermostat brands such as Nest and Tado. Navien also have their own Smart Plus Controller for perfect integration.

Engineering excellence

The Navien NCB range uses stainless steel heat exchangers. This prevents corrosion and reduces the risk of problems arising during the boilers’ lifespan.

Frost protection

A built-in sensor inside the boiler automatically detects the ambient temperature. It will start a safety heating cycle to prevent damage to internal equipment due to freezing temperatures.


We like Navien. They offer great service and products. Their gas boiler offering is impressive but quite expensive at the minute. The price may come down over time, but as it stands, we currently recommend Viessmann boilers for homes with natural gas or LPG. We do recommend Navien for oil boiler installations.

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