Navien NCB300-28K, Service Manual

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76 Troubleshooting
5.2.12 Error 302
Error conditions and checklist
Error Description
E302
Low water pressure
Low pressure faults are monitored by a water pressure sensor and when a fault is detected
the system displays E302 Low water level error is generated if water pressure is 0.5 bar or
less for 3 sec.
The error is automatically cancelled if water pressure returns to 0.5 bar or above.
Checklist
1. Check if the input water pressure sensor is wet for any reason, including leakage.
2. Check the auto feeder.
3. Check the controller.
Is there a leak inside the
boiler?
Is the water
pressure sensor
normal?
Check connections
Repair the leak
Replace the water pressure sensor
Yes
No
Yes
No
Testing method
Fault Possible causes Testing method
E302 Low water pressure
Check the water supply pressure (0.5 bar or lower is the error state).
Check if the safety valve is stuck.
Low water pressure
sensor
Water pressure sensor
fault
1. Check the output voltage. (Normal state: 0.25-4.93 V)
2. Replace the faulty or open water pressure sensor.