NSS Diagnostics and Troubleshooting 4

Question 1

A technician is diagnosing a Navien NPN-199 that displays E407 even after repressurizing the system. What should be checked next?

Accepted Answer

Verify the expansion tank pre-charge pressure and condition

Answer

If repressurizing does not resolve E407, a waterlogged or failed expansion tank cannot maintain system pressure, causing repeated pressure drops and the same error.

Question 2

What is the correct method to clear a hard lockout on a Navien NPE tankless water heater?

Accepted Answer

Press and hold the power button for 3 seconds or cycle power at the breaker

Answer

Navien hard lockouts are cleared by pressing the power button for 3 seconds or cycling the unit's circuit breaker after addressing the root cause.

Question 3

A Navien unit is installed in a direct-vent configuration but is drawing combustion air from the room. What error is most likely to result?

Accepted Answer

E003 — ignition failure due to oxygen-depleted combustion air

Answer

If the combustion air pipe is disconnected or improperly terminated, the unit may draw oxygen-depleted room air, causing unreliable ignition and E003 lockouts.

Question 4

When checking a Navien unit's gas valve, a technician measures 0V at the valve solenoid terminals during a call for heat. What does this indicate?

Accepted Answer

The PCB is not sending the activation signal to the valve

Answer

Zero voltage at the solenoid terminals during a heat call indicates the control board is not energizing the valve, pointing to a PCB or wiring fault rather than a valve failure.

Question 5

A Navien NHB combi-boiler is losing DHW temperature during simultaneous space heating demand. What is the most appropriate diagnostic step?

Accepted Answer

Check the diverter valve operation and priority switching logic in the installer settings

Answer

Simultaneous DHW and heating demand is managed by the diverter valve and priority logic; improper settings or a sluggish valve will cause DHW temperature to drop.

(NSS) Certified Navien Service Specialists Practice Test

(NSS) Certified Navien Service Specialists Practice Test

NSS Diagnostics and Troubleshooting 4