NSS Maintenance and Repair Techniques 3 — Questions and Answers
Question 1: What is the purpose of the condensate neutralizer in a Navien condensing unit and when should it be serviced?
- It removes chlorine from inlet water; replace every 5 years
- It raises the pH of acidic condensate before drain discharge; replace media when exhausted or annually (Correct answer)
- It prevents backflow of drain gases; clean monthly
- It filters particulates from combustion air; replace every 2 years
Correct answer: It raises the pH of acidic condensate before drain discharge; replace media when exhausted or annually
The condensate neutralizer raises the pH of acidic condensate to protect drains, and its media must be replaced when exhausted or at least annually.
Question 2: A Navien NPE-180S produces yellow-tipped flames visible through the sight glass. What is the correct immediate action?
- Increase the gas pressure to the unit
- Shut down the unit and inspect for combustion air restriction or gas-air ratio issues (Correct answer)
- Switch the unit to propane mode
- Reset the board and observe for recurrence
Correct answer: Shut down the unit and inspect for combustion air restriction or gas-air ratio issues
Yellow-tipped flames indicate incomplete combustion, which can produce dangerous CO levels; the unit should be shut down and the combustion air and gas-air ratio investigated.
Question 3: During a Navien boiler startup after a dry-fire prevention shutdown, what must a technician verify before restoring power?
- That the recirculation pump is off
- That all air is purged from the system and it is fully filled with water (Correct answer)
- That the condensate trap is empty
- That the outdoor sensor is unplugged
Correct answer: That all air is purged from the system and it is fully filled with water
Before restoring power after a dry-fire shutdown, the system must be fully filled and bled of air to prevent heat exchanger damage from overheating.
Question 4: On a Navien NFC-175 combi unit, the domestic hot water priority function means what during a DHW call?
- The space heating circulator continues at reduced speed
- Space heating output is suspended while domestic hot water demand is active (Correct answer)
- Both heating zones and DHW operate simultaneously at half capacity
- The unit switches to electric backup heating for DHW
Correct answer: Space heating output is suspended while domestic hot water demand is active
DHW priority suspends space heating output to dedicate full unit capacity to domestic hot water, ensuring adequate DHW temperature.
Question 5: A Navien unit repeatedly trips its high-limit temperature sensor. After ruling out scale buildup, what should the technician check next?
- The cold water inlet pressure
- Adequate flow rate through the unit and the recirculation pump operation (Correct answer)
- The gas meter capacity at the street
- The exhaust vent length
Correct answer: Adequate flow rate through the unit and the recirculation pump operation
Insufficient flow through the heat exchanger causes rapid temperature rise and high-limit trips; the technician should verify minimum flow rates and pump operation.
Question 6: When performing a gas pressure check on a Navien unit, where should the inlet pressure be measured?
- At the street meter only
- At the unit's gas valve inlet port using a manometer (Correct answer)
- At the first union fitting after the shut-off valve
- At the burner manifold pressure test port
Correct answer: At the unit's gas valve inlet port using a manometer
Static and operating inlet gas pressure must be measured at the gas valve inlet port to ensure the unit receives the manufacturer-specified supply pressure.
Question 7: What Navien diagnostic feature allows a technician to view real-time operational parameters such as flow rate, inlet/outlet temperatures, and fan RPM without disassembling the unit?
- The service mode accessible via the front panel or NaviLink app (Correct answer)
- The condensate drain inspection port
- The sight glass viewport
- The external pressure gauge port
Correct answer: The service mode accessible via the front panel or NaviLink app
Navien's service mode, accessible via the front panel or NaviLink app, displays live operational parameters to aid troubleshooting without disassembly.
NSS Maintenance and Repair Techniques 3
What is the purpose of the condensate neutralizer in a Navien condensing unit and when should it be serviced?