NSS Maintenance and Repair Techniques 5 — Questions and Answers
Question 1: A Navien NPE tankless unit installed in a cold climate shows freeze damage to the cold water inlet. The built-in freeze protection did not prevent it. What is the most likely reason?
- The freeze protection only works when the unit has power and is not tripped off (Correct answer)
- The inlet water pressure was too low to activate protection
- The freeze protection thermostat setpoint was too high
- The gas valve was open during freezing temperatures
Correct answer: The freeze protection only works when the unit has power and is not tripped off
Navien's built-in freeze protection requires the unit to be plugged in and powered; without power, the electric heating elements cannot activate to prevent freezing.
Question 2: When Navien service instructions specify purging air from a combi-boiler's heating loop, what is the correct sequence?
- Open all zone valves, then pressurize the system, then bleed each high point in order (Correct answer)
- Bleed radiators first, then close zone valves, then pressurize
- Pressurize to 30 PSI, then open drain valves at low points
- Fill with glycol first, then purge air at the expansion tank
Correct answer: Open all zone valves, then pressurize the system, then bleed each high point in order
Proper air purging requires opening all zone valves to allow flow, pressurizing the system, then bleeding from each high point in sequence to eliminate trapped air pockets.
Question 3: A Navien NPN boiler is losing system pressure repeatedly with no visible external leaks. What should the technician inspect next?
- The pressure relief valve for weeping or continuous discharge (Correct answer)
- The outdoor reset sensor calibration
- The modulating gas valve actuator
- The recirculation pump seal only
Correct answer: The pressure relief valve for weeping or continuous discharge
A pressure relief valve that weeps or discharges intermittently causes gradual system pressure loss that may not be visible as a continuous external leak.
Question 4: What does the Navien 'flow stabilizer' (buffer tank connection) accomplish in a low-mass radiant heating system?
- It prevents temperature swings by providing thermal mass to reduce short-cycling (Correct answer)
- It stores domestic hot water for high-demand periods
- It increases the working pressure of the system
- It filters particulates from the return water before the heat exchanger
Correct answer: It prevents temperature swings by providing thermal mass to reduce short-cycling
A buffer tank adds thermal mass to low-mass systems, smoothing out temperature swings and reducing boiler short-cycling that would otherwise occur.
Question 5: A Navien unit's dip switches are incorrectly configured after a board replacement. Which consequence is most likely if the cascade priority switch is set wrong in a multi-unit installation?
- One unit runs at 100% while others never fire, causing premature wear on the lead unit (Correct answer)
- All units fire simultaneously at minimum output regardless of demand
- The units default to domestic hot water mode only
- The expansion tanks on each unit over-pressurize
Correct answer: One unit runs at 100% while others never fire, causing premature wear on the lead unit
Incorrect cascade priority settings can cause one unit to run continuously as the permanent lead while follower units never activate, creating uneven wear.
Question 6: When a Navien service bulletin calls for a firmware update to correct a modulation control issue, what is the required method for updating the unit's control board firmware?
- Replace the control board entirely with a pre-flashed board from Navien
- Use the NaviLink Wi-Fi module or Navien's field service tool connected to the service port (Correct answer)
- Download firmware to a USB drive and insert it into the front panel USB slot
- Call Navien tech support who remotely pushes the update over the internet
Correct answer: Use the NaviLink Wi-Fi module or Navien's field service tool connected to the service port
Navien firmware updates are performed via the NaviLink module (over Wi-Fi) or using Navien's dedicated field service update tool connected to the unit's service port.
Question 7: After completing repairs on a Navien unit and restoring gas, what is the correct final verification step before leaving the installation?
- Visually confirm the flame through the sight glass only
- Perform a leak check on all disturbed gas connections using an approved leak detection method, then observe a full operating cycle (Correct answer)
- Reset all error codes and leave the unit running
- Check the water pressure gauge reads above 10 PSI
Correct answer: Perform a leak check on all disturbed gas connections using an approved leak detection method, then observe a full operating cycle
All disturbed gas connections must be leak-tested using an approved detection method, followed by observing a complete operating cycle to confirm normal unit performance.
NSS Maintenance and Repair Techniques 5
A Navien NPE tankless unit installed in a cold climate shows freeze damage to the cold water inlet.
The built-in freeze protection did not prevent it.
What is the most likely reason?