NSS Installation and Setup Procedures 4 — Questions and Answers
Question 1: When installing a Navien unit in a mobile home, which additional requirement applies compared to a standard residential installation?
- The unit must be installed outdoors only
- The unit must be listed and approved for mobile home installation (Correct answer)
- The unit must use LP gas only
- The unit requires a 240V electrical connection
Correct answer: The unit must be listed and approved for mobile home installation
Units installed in mobile homes must carry a listing and approval specifically for mobile home use per HUD and manufacturer requirements.
Question 2: Which Navien service menu function is used to manually purge air from the water circuit after initial installation?
- Maintenance mode → pump purge cycle (Correct answer)
- Error reset mode
- Factory reset sequence
- Gas valve test mode
Correct answer: Maintenance mode → pump purge cycle
The pump purge cycle in maintenance mode runs the internal pump to purge trapped air from the water circuit.
Question 3: What is the correct orientation for installing the Navien NPE series unit's intake and exhaust vent pipes when using a concentric vent kit?
- Exhaust in center pipe, intake in outer pipe (Correct answer)
- Intake in center pipe, exhaust in outer pipe
- Both pipes carry mixed air/exhaust simultaneously
- Either orientation is acceptable per local code
Correct answer: Exhaust in center pipe, intake in outer pipe
In a concentric vent configuration, exhaust travels through the inner center pipe while combustion air enters through the outer annular space.
Question 4: During a Navien combi-boiler installation, what is the minimum expansion tank size recommendation for a typical residential heating system?
- 2-gallon tank
- 4.4-gallon tank (Correct answer)
- 10-gallon tank
- No expansion tank is required for Navien combi systems
Correct answer: 4.4-gallon tank
Navien recommends a minimum 4.4-gallon expansion tank for residential hydronic heating systems connected to a combi-boiler.
Question 5: What is the purpose of the NPE series 'buffer tank sensor' input on the Navien PCB?
- Monitors outdoor ambient temperature for weather compensation
- Reads the temperature of a buffer or storage tank to control space heating output (Correct answer)
- Detects freezing conditions in the condensate line
- Measures incoming cold water temperature for set-point adjustment
Correct answer: Reads the temperature of a buffer or storage tank to control space heating output
The buffer tank sensor input allows the Navien unit to monitor tank temperature and modulate output to maintain target heating setpoints.
Question 6: Which fitting must be installed on the hot water outlet of a Navien tankless water heater to allow for thermal expansion in a closed plumbing system?
- Pressure-reducing valve (PRV)
- Thermal expansion tank or expansion relief device (Correct answer)
- Backflow preventer without bypass
- Check valve rated at 150 PSI
Correct answer: Thermal expansion tank or expansion relief device
A thermal expansion tank is required on closed plumbing systems to absorb pressure increases caused by thermal expansion.
Question 7: When configuring a Navien NFC-200 for a domestic hot water priority zone, what sequence does the unit follow when both space heating and DHW are called simultaneously?
- Space heating takes priority over DHW
- DHW is prioritized and space heating is temporarily suspended (Correct answer)
- Both demands are served simultaneously at reduced capacity
- The unit shuts down and displays an error code
Correct answer: DHW is prioritized and space heating is temporarily suspended
Navien combi-boilers prioritize DHW over space heating to ensure adequate hot water supply during simultaneous demand.
NSS Installation and Setup Procedures 4
When installing a Navien unit in a mobile home, which additional requirement applies compared to a standard residential installation?