NSS Installation and Setup Procedures 5 — Questions and Answers
Question 1: What is the maximum vent length for a Navien NPE-240A2 using 4-inch PVC pipe in a two-pipe direct vent configuration?
- 25 equivalent feet
- 50 equivalent feet
- 75 equivalent feet (Correct answer)
- 100 equivalent feet
Correct answer: 75 equivalent feet
The NPE-240A2 allows up to 75 equivalent feet of 4-inch vent piping in a two-pipe direct vent configuration.
Question 2: When connecting a Navien unit to a recirculation loop using the built-in pump, which setting controls the recirculation temperature differential?
- The temperature set-point dial on the front panel
- The ΔT parameter in the service menu (Correct answer)
- The DIP switch 4 ON/OFF position
- The external thermostat wired to the CNH terminals
Correct answer: The ΔT parameter in the service menu
The ΔT (delta-T) parameter in the Navien service menu sets the temperature differential at which the recirculation pump activates.
Question 3: Which Navien installation step is required when the unit is installed where the gas supply line contains significant moisture or debris?
- Install a sediment trap and drip leg upstream of the unit's gas inlet (Correct answer)
- Install a moisture separator on the exhaust vent
- Pre-run the unit for 30 minutes before lighting the burner
- Bypass the gas valve to allow moisture to pass freely
Correct answer: Install a sediment trap and drip leg upstream of the unit's gas inlet
A sediment trap and drip leg must be installed upstream of the gas inlet to prevent moisture and debris from entering the gas valve.
Question 4: During initial startup of a Navien unit, the installer notices error code 003E. What does this indicate?
- Ignition failure after three attempts (Correct answer)
- Abnormal exhaust temperature detected
- No water flow detected at startup
- Gas valve not opening properly
Correct answer: Ignition failure after three attempts
Error code 003E on Navien units indicates ignition failure after the unit has attempted ignition multiple times without confirming a flame.
Question 5: What is the function of the 'flow sensor' in a Navien tankless water heater during the installation and commissioning phase?
- Measures gas flow to the burner assembly
- Detects water flow to trigger unit activation and measure GPM (Correct answer)
- Monitors exhaust gas flow for combustion efficiency
- Detects recirculation pump flow rate
Correct answer: Detects water flow to trigger unit activation and measure GPM
The flow sensor detects when water is flowing through the unit and measures GPM to trigger activation and modulate burner output.
Question 6: When installing a Navien unit in an area with hard water (above 11 grains per gallon), what installation measure is strongly recommended by Navien?
- Install a whole-house water softener or scale inhibitor upstream of the unit (Correct answer)
- Install a bypass valve around the unit and use it periodically
- Increase the temperature set-point to prevent scale buildup
- Flush the unit with acid immediately after installation
Correct answer: Install a whole-house water softener or scale inhibitor upstream of the unit
Navien recommends installing a water softener or scale inhibitor when water hardness exceeds 11 GPG to protect the heat exchanger.
Question 7: Which Navien feature allows the unit to communicate with a building automation system (BAS) or smart thermostat using a 0-10V analog signal?
- The cascade communication port
- The CNH analog input terminal
- The BMS/0-10V input on the PCB (Correct answer)
- The external DHW sensor port
Correct answer: The BMS/0-10V input on the PCB
The BMS/0-10V analog input on the Navien PCB allows external building automation systems to modulate the unit's output capacity.
NSS Installation and Setup Procedures 5
What is the maximum vent length for a Navien NPE-240A2 using 4-inch PVC pipe in a two-pipe direct vent configuration?