NSS Diagnostics and Troubleshooting 3

Question 1

A Navien NPE-240A2 shows intermittent E003 errors during peak demand. After verifying gas supply is adequate, what should be checked next?

Accepted Answer

Spark igniter gap and electrode condition

Answer

Intermittent ignition failures during high demand often result from a worn or improperly gapped igniter electrode that cannot reliably produce spark.

Question 2

A customer reports their Navien combi unit heats domestic hot water correctly but the radiant floor heating is cold. What is the most likely cause?

Accepted Answer

Failed diverter valve not switching to heating mode

Answer

A failed diverter valve will prevent the unit from switching flow from the DHW circuit to the central heating circuit, leaving radiant heat cold while DHW works.

Question 3

What resistance value should a properly functioning Navien inlet water thermistor read at approximately 77°F (25°C)?

Accepted Answer

10,000 ohms

Answer

Navien NTC thermistors typically read approximately 10,000 ohms (10 kΩ) at 25°C; deviation from this value indicates a faulty sensor.

Question 4

A Navien boiler's condensate line is frozen. What is the correct field remedy to prevent recurrence?

Accepted Answer

Insulate and pitch the condensate line correctly, adding heat trace if necessary

Answer

Frozen condensate lines must be insulated and properly pitched toward the drain; heat trace tape should be added in areas exposed to freezing temperatures.

Question 5

During startup, a Navien unit's combustion fan runs but the gas valve does not open. What should the technician check first?

Accepted Answer

Inspect the pressure switch proving fan operation

Answer

The gas valve requires a proven fan signal from the pressure switch before it will open; a faulty pressure switch will prevent gas valve activation even with the fan running.

(NSS) Certified Navien Service Specialists Practice Test

(NSS) Certified Navien Service Specialists Practice Test

NSS Diagnostics and Troubleshooting 3