E302 Low water pressure

What the control is telling you

The built-in pressure-sensing low water cutoff saw system pressure below the low limit (default 6 psi). Needs a manual reset after the cause is fixed.

Applies to: Navien NHB-H (NHB-055H/080H/110H/150H) and NFB-H fire-tube (NFB-175H/200H) condensing boilers

Likely causes

• System pressure too low (leak, relief valve discharge, not filled)
• Air in system
• Expansion tank problem
• Low Sys Pressure parameter set too high

Test and repair steps

1. Read Water Press in Status Info and check the system gauge.
2. Refill to the design pressure (typical cold fill 12 psi for residential); NHB-H operates at 12-30 psi.
3. Find and repair leaks; constant make-up water damages the heat exchanger.
4. Check the expansion tank charge and size and the relief valve for discharge.
5. Check parameter 16 Low Sys Pressure (range 4-17 psi, default 6 psi).
6. Reset the boiler with the Back button once pressure is restored.

Settings for these units

Installation clearances (indoor) · Navien NHB-H

Bracket gives 5/8 in (16 mm) from the wall; studs at 16 in on centre.

Common vent installs: 36 in above the top and 24 in in front are recommended for service.

Installation clearances (indoor) · Navien NFB-H

Do not install on carpet; indoors only.

Remove the wood pallet and refit the 6 screws to keep the cabinet airtight.

Models that show this code

6 models in Navien NHB-H, Navien NFB-H

Other codes on the same units

• E218 Heating return temperature sensor
• E278 External system supply sensor not detected
• E279 External system return sensor not detected
• E291 Return temperature higher than supply
• E352 High water pressure
• E353 Water pressure sensor fault
• E480 DHW tank sensor not detected
• E515 PCB fault