What does the fault code E302 for NCB-CE or NCB300 mean?
October 24th 2023
E302 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 (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).
More news articles...

Aug 27th 2025
Blog posts
Revolutionary A+ Energy Rating Oil Boiler Now Comes with £100 Installer Cashback
Navien UK has launched an exclusive cashback promotion that’s transforming the oil boiler installation market. The LCB700 Blue Flame range

Aug 18th 2025
Advice
How to Set Up Your Navien NCB500 ON Combi Boiler: Complete Installation Guide
If you’ve just had a Navien NCB500 ON installed, you’re probably eager to get it up and running. This compact

Jul 31st 2025
News
Introducing the Game-Changing Navien NCB500 System Boiler
Looking for a heating solution that combines power, efficiency, and smart technology in one compact package? We’re thrilled to introduce