NCB500 ON Combi Boiler for Installers
Our compact NCB500 ON combi boiler offers fast and flexible installation options – making it a great option for family homes that require a quick heating solution. Every Navien Combi Boiler features high-quality components to provide exceptional levels of reliability and performance.
What is ON technology?
Navien ON technology maximises the recirculation of domestic hot water whilst reducing water wastage – this means that boilers with ON technology can deliver instant and consistent hot water.

Technical Data
Shower rating
Heat Output
DHW
Modulation
Flue
Weight
Dimensions
ErP Efficiency
ErP Efficiency with Smart Plus (x3)
NOx Classification
Downloads
A successful NCB700 installation in East Sussex
(1.26 MB)

An energy efficient ‘crossover’ combi installation.
(1.83 MB)

Case Study: Historic Grade I residence
(874.95 KB)

Case Study: Preston property receives heating upgrade
(500.69 KB)

Case Study: Upgrade for Grade II listed home
(1.27 MB)

NCB700 ON / 500 ON / 300 brochure
(13.13 MB)

NCB500 IOM manual – Combi
(31.5 MB)

NCB500 Service Manual – Combi
(34.57 MB)

NCB500 User Manual – Combi
(2.91 MB)

NCB300/500 ON Stand off Kit Installation manual
(333 KB)
NCB300/500 ON Pipe Cover Installation manual
(4.12 MB)
NCB500 ON Combi Boiler for Installers
What does the fault code E302 for NCB500 or NCB700 mean?
E302 means that the system pressure is too low and you may see that the system pressure gauge or on the front display indicates that the pressure in the system is below the 1 bar pressure.
To re-pressurise the system, you will find a NaviFill Link (a plastic and brass link with a green plastic leaver) on the underside of the boiler.
The green leaver needs to be pulled down slowly. The water will start to refill the system (water should be heard filling the system). You should see the pressure gauge or the pressure reading on the display rise back up between 1 bar and 1.2 bar pressure and then stop filling.
Once the pressure gauge or pressure reading on the display is between 1 bar and 1.2 bar release the green leaver and the water will stop filling the system. The error code E302 will stop and the boiler will now operate. If the error code E302 is still active, fill up the system a little more but not over 1.5 bar.
(If you do fill the system too much and the pressure gauge is too high, just bleed water from a radiator until the pressure on the gauge goes down to below 1.2 bar).






