Navien NCB300 Combi Gas Condensing Boiler

NCB300 The Impressive Entry level

The NCB300 gas condensing combi boiler is our entry model, which offers the same hot water comfort, powerful heating and flexible installation options as larger models, but in a compact design. This combination of features makes the NCB300 gas boiler an excellent choice for smaller properties where exceptional levels of reliability and DHW performance are the priority.

  • ErP A+ energy efficiency rating for ultra-low running costs*
  • IPX5 rating provides protection from any water leaks
  • Smartphone compatible offering remote adjustments of heating and hot water systems
  • Smart weather forecasting and Geofencing maximise efficiencies and convenience
  • 5-year parts and labour warranty for complete peace of mind
  • Extended venting up to 8m
  • Stainless steel heat exchangers for optimum durability and long term efficiencies
  • Hydrogen-ready (20% blend) technology for futureproofing

* An A+ energy rating is achieved when installed with 3 Smart Plus room thermostats.

Technical Data

NCB300-28K NCB300-37K NCB300-41K
Shower rating Number of showers One shower Two showers Two showers & one tap
Heat Output Heat input range 24.7/4.3 26.8/4.6 26.8/4.6
Modulation (max/min) 6:1 6:1 6:1
Heat output range @ 80/60°C 24.0/4.2kW 26.0/4.5kW 26.0/4.5kW
DHW DHW heat input range 28.0/4.3kW 37.0/4.6kW 41.0/4.6kW
DHW output range 28.0/4.3kW 37.0/4.6kW 41.0/4.6kW
DHW flow rate @ 25°C temp. rise. 16.0 l/min 21.3 l/min 23.6 l/min
DHW flow rate @ 35°C temp. rise. 11.5 l/min 15.2 l/min 16.8 l/min
DHW flow rate for kitchen @ 45°C temp. rise. 9.0 l/min 11.8 l/min 13.1 l/min
Modulation TDR 7:1 8:1 9:1
Flue Flue Size Coaxial length Ø 60/100
Max. horizontal coaxial length Ø60/100 8m
Max. vertical coaxial length Ø60/100 8m
Weight Lift weight 29kg 33kg 33kg
Dimensions Width x Depth x Height 395 x 285 x 680mm
ErP Efficiency ErP A (93%)
ErP Efficiency with Smart Plus (x3) ErP A+ (98%)
NOx Classification Class 6

Navien NCB300 Gas Condensing Boiler FAQs

What does the fault code E302 mean for the NCB300?

E302 This means that the system pressure is too low and you may see that the system pressure gauge indicates that the pressure in the system is below the 1 bar pressure. To re-pressurise the system you will find a filling loop (copper ‘U’ shaped tube with two nuts at each end) on the underside of the boiler or a metal braided flexible hose external of the boiler on the pipework with one or two tap connections at either end of the filling loop.

The tap or taps should be opened a quarter of a turn and the water will start to refill the system (water should be heard filling the system). You should see the pressure gauge rise back up between 1 bar and 1.7 bar pressure and then stop filling. Boiler information on water pressure can also be seen on the digital display by pressing the Eco button for 6 seconds and then scroll through to ‘A6’ which will display the water pressure.

Once the pressure gauge between 1 bar and 1.7 bar turn the taps back to the off position and the water will stop filling the system. The error code 118 will stop and the boiler will now operate. If the error code 118 is still active, fill up the system a little more but not over 2.0 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 1.7 bar).

To re-pressurise the system you will find a filling loop (metal braided flexible hose) on the underside of the boiler with two tap connections at either end of the filling loop. One small blue & one small black tap handles.

The taps should be opened a quarter of a turn. Open the small black one and then open slowly the small blue one. The water will start to refill the system (water should be heard filling the system). You should see the pressure gauge rise back up between 1 bar and 1.2 bar pressure and then stop filling.

Once the pressure gauge is between 1 bar and 1.2 bar turn the taps back to the off position 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).

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