NSS Maintenance and Repair Techniques 4 — Questions and Answers
Question 1: A Navien NPE unit installed on LP gas is producing soot on the heat exchanger after only six months. What is the most likely root cause?
- The unit was not converted to LP operation and orifices remain sized for natural gas (Correct answer)
- The exhaust vent is too short
- The cold water supply pressure is too high
- The flow sensor is reading incorrectly
Correct answer: The unit was not converted to LP operation and orifices remain sized for natural gas
If the unit was not properly converted to LP (propane) with correct orifices and pressure settings, rich combustion results in soot formation on the heat exchanger.
Question 2: Which Navien error code specifically indicates a problem with the exhaust thermistor or an over-temperature exhaust condition?
- E004
- E012
- E030 (Correct answer)
- E109
Correct answer: E030
Error code E030 on Navien units indicates an exhaust high-temperature condition or exhaust thermistor fault, signaling a potential venting or combustion issue.
Question 3: When replacing a Navien primary heat exchanger, what must be done with the condensate drain tubing connections after reassembly?
- They should be capped permanently
- They must be reconnected and tested for leaks before firing the unit (Correct answer)
- They should be routed to the exterior only
- They require no action as they self-connect
Correct answer: They must be reconnected and tested for leaks before firing the unit
After reassembly, condensate drain tubing must be properly reconnected and leak-tested to prevent acidic condensate from draining onto electrical or gas components.
Question 4: A Navien recirculation pump runs continuously but no hot water is delivered at the fixture. What should the technician verify first?
- Whether the pump direction/impeller rotation matches the system flow direction (Correct answer)
- Whether the DHW setpoint is below 120°F
- Whether the gas supply is off
- Whether the cold water shutoff is partially closed
Correct answer: Whether the pump direction/impeller rotation matches the system flow direction
A recirculation pump installed with incorrect flow direction will not move water through the loop, causing no hot water delivery despite the pump running.
Question 5: What is the correct procedure for priming the condensate trap on a Navien condensing unit during initial startup?
- Leave it dry so condensate fills it naturally over the first heating cycle
- Fill the trap with water before startup to establish the liquid seal (Correct answer)
- Fill with antifreeze to prevent freezing
- Blow air through it to verify no blockage, then leave empty
Correct answer: Fill the trap with water before startup to establish the liquid seal
The condensate trap must be filled with water before startup to create a proper liquid seal that prevents flue gases from escaping through the drain line.
Question 6: During a Navien heat exchanger cleaning, a technician notices white crystalline deposits that do not dissolve in vinegar. What do these deposits likely indicate?
- Silica scale from high silica content water requiring professional descaling compounds (Correct answer)
- Normal calcium carbonate scale that needs longer soak time
- Combustion byproduct soot solidified with moisture
- Corrosion from galvanic action with dissimilar metals
Correct answer: Silica scale from high silica content water requiring professional descaling compounds
Silica scale does not dissolve in vinegar or citric acid and requires specialized descaling compounds; it often indicates very high-silica source water.
Question 7: After replacing a Navien gas valve, which parameter must be verified using a manometer at the burner manifold pressure test port?
- Static gas supply pressure only
- Manifold (outlet) pressure at minimum and maximum fire to confirm proper modulation (Correct answer)
- Return water temperature differential
- Fan RPM at high fire
Correct answer: Manifold (outlet) pressure at minimum and maximum fire to confirm proper modulation
Manifold pressure must be verified at both minimum and maximum fire conditions to confirm the new gas valve modulates correctly per Navien specifications.
NSS Maintenance and Repair Techniques 4
A Navien NPE unit installed on LP gas is producing soot on the heat exchanger after only six months.
What is the most likely root cause?