Navien NHB-055 Guide

WARNING
If the information in these instructions is not followed exactly, a fire or explosion may result, causing
property damage, personal injury, or death.
Do not store or use gasoline or other flammable vapors and liquids in the vicinity of this or any other
appliance.
WHAT TO DO IF YOU SMELL GAS
Ɣ
Do not try to light any appliance.
Ɣ
Do not touch any electrical switch; do not use any phone in your building.
Ɣ
Immediately call your gas supplier from a neighbor’s phone. Follow the gas supplier’s instructions.
Ɣ
If you cannot reach your gas supplier, call the fire department.
Installation and service must be performed by a qualified installer, service agency or the gas
supplier.
Keep this manual near this boiler for future
reference whenever maintenance or service
is required.
NHB Condensing Boiler
User’s Information Manual
Model
NHB-055
NHB-080
NHB-110
NHB-150

2 Contents
Contents
1. Safety Information 3
2. About the Boiler 5
2.1 Description of the Boiler 5
2.2 Parts of the Boiler 5
2.3 The Front Panel 6
3. Operating the Boiler 8
3.1 Turning the Boiler On or Off 8
3.2 Adjusting the Temperature 8
3.3 Viewing Basic Information 9
3.4 Resetting the Boiler 10
4. Maintaining the Boiler 11
4.1 Cleaning the Boiler 11
4.2 Draining the Boiler 11
4.3 Cleaning the Air Intake Filter 12
4.4 Protecting the Boiler from Freezing 14
4.5 Maintenance Schedules 14
5. Troubleshooting 19
5.1 Solving Basic Problems 19
5.2 Understanding Error Codes 20

Safety Information 3
WARNING
If you do not follow these instructions exactly, a fire or explosion
may result causing property damage, personal injury or loss of
life.
A. This appliance does not have a pilot. It is equipped with an
ignition device which automatically lights the burner. Do
not try to light the burner by hand.
B. BEFORE OPERATING smell all around the appliance area for
gas. Be sure to smell next to the floor because some gas is
heavier than air and will settle on the floor.
WHAT TO DO IF YOU SMELL GAS
ƔDo not try to light any appliance.
ƔDo not touch any electric switch; do not use any phone
in your building.
ƔImmediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
ƔIf you cannot reach your gas supplier, call the fire
department.
ƔDo not return to your home until authorized by your
gas supplier or the fire department.
C. Do not use this appliance if any part has been under water.
Immediately call a qualified service technician to inspect
the appliance and to replace any part of the control system
and any gas control which has been under water.
The following safety symbols are used in this manual. Read and
follow all safety instructions in this manual precisely to avoid
unsafe operating conditions, fire, explosion, property damage,
personal injury, or death. Keep this manual for future reference.
DANGER
Indicates an imminently hazardous situation which, if not
avoided, could result in severe injury or death.
WARNING
Indicates a potentially hazardous situation which, if not
avoided, may result in injury or death.
CAUTION
Indicates a potentially hazardous situation that, if not avoided,
could result in property damage.
1. Safety Information

4 Safety Information
CAUTION
ƔDo not attempt to repair or replace any part of the boiler,
unless it is specifically recommended in this manual.
For all other service, contact an authorized technician or
licensed professional. Improper adjustments, alterations,
service, or maintenance may lead to property damage,
personal injury, or death and will void your warranty.
ƔDo not operate the boiler if you feel something is wrong
with it.
Doing so may result in product damage or personal injury.
ƔDo not allow children to operate or access the boiler.
Doing so may result in product damage or personal injury.
ƔDo not turn on the boiler unless the water and gas
supplies are fully opened.
Doing so may damage the boiler.
ƔDo not use this boiler for anything other than its
intended purpose, as described in this manual.
ƔDo not remove the front cover unless the power to the
boiler is turned off or disconnected.
Failure to do so may result in electric shock.
ƔWhen servicing the controls, label all wires prior to
disconnecting them.
Failure to do so may result in wiring errors, which can lead to
improper or dangerous operation.
ƔDo not use unapproved replacement or accessory parts.
Doing so may result in improper or dangerous operation
and will void the manufacturer’s warranty.
ƔDo not place anything in or around the vent terminals,
such as a clothes line, that could obstruct the air flow in
or out of the boiler.
ƔThis boiler has been approved for use in the USA and
Canada only.
Using the boiler in any other country will void the
manufacturer’s warranty.
ƔShould overheating occur or the gas supply fail to shut
off, turn off the manual gas valve to the appliance.
WARNING
ƔShut off the gas supply if the boiler is damaged.
Have your installer or plumber show you the location of the
gas shut off valve and demonstrate how to close the valve.
If the boiler is damaged as a result of overheating, fire, flood,
or any other reason, close the manual shut off valve and do
not operate the boiler again until it has been inspected by a
qualified technician.
ƔDo not store or use gasoline or other flammable liquids
near this boiler.
Doing so may result in fire or explosion.
ƔDo not place combustibles, such as newspapers or
laundry, near the boiler or venting system.
Doing so may result in a fire.
ƔDo not place or use hair sprays, spray paints, or any other
compressed gases near the boiler or venting system,
including the vent termination.
Doing so may result in fire or explosion.
ƔDo not operate the boiler with the front cover opened.
Doing so may result in fire or carbon monoxide (CO)
poisoning, which may result in property damage, personal
injury, or death.
ƔDo not operate this boiler without proper venting.
Doing so may result in fire or carbon monoxide (CO)
poisoning, which may result in property damage, personal
injury, or death. Inspect the vent termination and air intake
supply annually to ensure proper operation of the boiler.
Turn off and discontinue use of the boiler if any of the vent
pipes, vent elbows, or intake pipes are damaged in any way,
separated at a joint, or show evidence of corrosion, rusting,
or melting.
ƔDo not touch the power cord or internal components of
the boiler with wet hands.
Doing so may result in electric shock.
ƔDo not make any electrical connections before turning
off the electrical power supply at service entrance panel.
Doing so may result in severe personal injury or death.

About the Boiler 5
2.2 Parts of the Boiler
2.2.1 Front View
Exhaust
Gas Vent
Combustion
Air Intake
2.2.2 Bottom View
a
b
c
d
e
# Description
a Rubber Grommets
b Condensate Outlet
c Gas Connection
d Space Heating Supply Connection
e Space Heating Return Connection
2.1 Description of the Boiler
The Navien NHB boiler is available in 4 models: NHB-055, NHB-080,
NHB-110 and NHB-150.
The main features are as follows:
ƔPower Interruption: When the power is restored after a power
failure, the boiler will automatically start and return to normal
operation. A manual reset is not required.
ƔFreeze Protection: A sensor inside the boiler automatically
detects the temperature and, if necessary, initiates a safety
heating cycle to prevent internal equipment damage due to
freezing temperatures.
ƔShort-Circuit Protection: Any short-circuit occurring in the
boiler’s electrical circuit immediately blows the internal glass
fuses and automatically cuts off the gas supply.
ƔLightning Protection: Each boiler is specially grounded, both
internally and externally, to protect against lightning strikes.
ƔCarbon Monoxide Protection: The boiler is designed to maintain
a safe air-to-gas ratio and combustion rate. This function is
continuously monitored by the boiler’s air ratio control module.
ƔAuto Fan Detection: The rotation of the fan is automatically
detected and controlled. Fan failure will stop the operation of
the boiler.
ƔBoiling Prevention: Excessive temperatures will automatically
stop the boiler.
2. About the Boiler

6 About the Boiler
2.3 The Front Panel
The front panel allows you to adjust the temperature and view the operating status or error codes. Remove the protective sheet from the front
panel before using it.
2.3.1 Icons and Digital Display
The icons and digital display on the front panel provide important
information required for the boiler’s operation. Refer to the
following table for detailed information.
a
Space heating mode
f
S
Supply water control
Indicates space heating mode operation. Indicates supply water control status.
b
Error
g
R
Return water control
A code will appear on the display. Indicates return water control status.
c
Combusting
h
O/R
Outdoor Reset
Indicates burner operation. Indicates outdoor reset operation.
d
DHW mode
i
Pri
Pri
Indicates DHW mode operation. Indicates DHW priority operation.
e
Digital Display
j
psi
Psi
Indicates water pressure.
b
a
f
g
h
c
d
e
i
j

About the Boiler 7
2.3.2 Buttons
Using the buttons on the front panel, you can turn on or off the
boiler, monitor the current operation status, and set the values
required for the boiler’s operation, such as space heating and DHW
supply temperatures. Refer to the following table for detailed
information.
k
Diagnostics button
n
Up button
For installers only Increases the temperature.
l
MODE
Mode button
O
Down button
Changes the mode. Decreases the temperature.
m
Reset button
p
Power button
Resets the boiler (if an error occurs). Turns the boiler on or off.
k
l
m
n
o
p

8 Operating the Boiler
2. Press the + (Up) or – (Down) buttons until the desired
temperature appears on the display.
MODE
You can adjust the temperature while the display is flashing. Once
the display stops flashing, the temperature setting is stored.
Note ƔThe Outdoor Reset Control will take precedence over
this temperature setting.
ƔIn case of outdoor reset sensor malfunction, the
boiler will operate at this set temperature.
ƔTake note of the original heating temperature in case
you want to restore it to the default.
ƔThe default space heating supply water temperature
range is 104°F (40°C, Absolute MIN) to 180°F (82°C,
Absolute MAX).
ƔThe default space heating return water temperature
range is 86°F (30°C, Absolute MIN) to 149°F (65°C,
Absolute MAX).
ƔYou can adjust the temperature range in the
parameter settings menu.
ƔThe boiler will retain your settings during a power
outage.
3.1 Turning the Boiler On or Off
To turn the boiler on or off, press the Power button for 0.3 seconds.
MODE
When the power is on, the boiler supply water temperature will
appear with the water pressure on the front panel display in
5 second intervals.
Note When displaying the boiler supply water temperature,
the supply or return water icon turns on, depending on
the space heating control mode.
3.2 Adjusting the Temperature
3.2.1 Adjusting the Space Heating Temperature
To adjust the heating temperature:
1. Press the Mode button once. The space heating mode icon
turns on.
MODE
3. Operating the Boiler

Operating the Boiler 9
3.3 Viewing Basic Information
To view information about the boiler, press the Mode button three
times.“INFO” will appear on the display.
MODE
Press the + or – buttons to switch between the information types.
Display Description
psi
O/R
SRPri
Space heating supply water
temperature (°F)
psi
O/R
SRPri
Space heating return water
temperature (°F)
psi
O/R
SRPri
Outdoor air temperature (°F)
(from Outdoor Temperature Sensor)
psi
O/R
SRPri
Outdoor reset curve
-: Not in use.
1: Finned tube baseboard
2: FAN coil
3: Cast iron baseboard
4: Low mass radiant
5: High mass radiant
6: Radiator
7: Custom (set by installer)
3.2.2 Adjusting the DHW Indirect Supply
Temperature
To adjust the water temperature:
1. Press the Mode button twice. The DHW mode icon turns on.
2. Press + (Up) or – (Down) buttons until the desired temperature
appears on the display.
MODE
You can adjust the temperature while the display is flashing. Once
the display stops flashing, the temperature setting is stored.
Note ƔTake note of the original DHW temperature in case
you want to restore it to the default.
ƔThe default DHW temperature range is 104°F (40°C,
Absolute MIN) to 180°F (82°C, Absolute MAX).
ƔYou can adjust the temperature range in the
parameter settings menu.
ƔThe boiler will retain your settings during a power
outage.

10 Operating the Boiler
3.4 Resetting the Boiler
If an error message appears, you can try resetting the boiler to
resolve the problem. To reset the boiler, press the Reset button.
MODE
If resetting the boiler does not solve the problem, refer to the
Troubleshooting section of this manual or contact Technical
Support at 1-800-519-8794.
Display Description
psi
O/R
SRPri
Boost interval time (set by installer)
psi
O/R
SRPri
Space heating water pressure in PSI
psi
O/R
SRPri
DHW priority time
psi
O/R
SRPri
System supply water temperature
(°F) (with optional temperature
sensor)
psi
O/R
SRPri
System return water temperature
(°F) (with optional temperature
sensor)
To exit the Information mode, press the Reset button.

Maintaining the Boiler 11
4.1 Cleaning the Boiler
CAUTION
Make sure the boiler is turned off and the power supply is
disconnected before cleaning the boiler. The boiler may
remain hot for several minutes after it is turned off. To prevent
burns, wait until the boiler has cooled down before cleaning.
To clean the boiler, wipe the outside with a damp cloth. Use a non-
acidic, non-abrasive cleaner to remove any surface stains. The front
panel is moisture resistant, but it is not waterproof. Keep it as dry
as possible.
4.2 Draining the Boiler
You will need to drain the boiler before performing maintenance
tasks, such as to prevent the boiler from freezing when it will not
be used for an extended period.
Refer to“2.2 Parts of the Boiler” on page 5 for details about part
locations.
To drain the boiler:
1. Place a bucket under the boiler to collect the residual water
inside the boiler.
2. Press the Power button on the front panel to turn off the boiler.
MODE
3. Close the gas valve.
Gas Valve
Open Closed
4. Close the water supply valve and the return valves on the
manifold system.
4. Maintaining the Boiler

12 Maintaining the Boiler
4.3 Cleaning the Air Intake Filter
If the air intake filter becomes clogged by dust or lint, the boiler
will cease to operate and“Error Code 110” will appear on the front
panel display. To properly maintain the boiler, clean the air intake
filter every 3-4 months.
To clean the air intake filter:
1. Press the Power button on the front panel to turn off the boiler.
MODE
2. Disconnect the power supply to the boiler.
3. Remove the front cover of the boiler.
5. Remove the drain cap on the manifold system to drain the
boiler.
Drain Cap
Drain Cap
Note ƔPlace a bucket under the boiler to gather water
released from the manifold system.
ƔDo not allow the pump to become wet.

Maintaining the Boiler 13
4. Remove the screw that secures the air intake filter (the filter is
located at the top left of the boiler).
5. Pull the filter out of the boiler.
6. Remove the filter from the plastic assembly. Dust and rinse it
with clean running water.
7. Allow the filter to dry completely.
8. Place the filter assembly back into the boiler and secure it with
the screw.
9. Replace the front cover.
10. Reconnect the power supply to the boiler.
11. Press the Power button on the front panel to turn on the boiler.

14 Maintaining the Boiler
4.5 Maintenance Schedules
Owner maintenance
Daily
ƔCheck the boiler area is free of
combustible/flammable materials and
air contaminants.
ƔCheck the pressure/temperature
gauge for signs of higher than normal
pressure.
Monthly
ƔVisually inspect the vent piping for
signs of leakage and blockage.
ƔVisually inspect the burner flames.
ƔInspect the condensate trap and the
PVC fittings.
Periodically ƔTest the LWCO for proper operation.
Every 6 months
ƔInspect boiler piping (gas and water)
for leaks.
ƔTest to make sure the relief valve is
operating normally.
Non-heating
season
ƔShut boiler down (unless boiler is used
for domestic hot water).
Service technician (See the following instructions)
Annual Start-up
General:
ƔAddress reported problems.
ƔInspect interior; clean and vacuum if
necessary.
ƔClean condensate trap and fill with
fresh water.
ƔCheck for leaks (water, gas, flue,
condensate).
ƔVerify flue and air lines in good
condition and sealed tight.
ƔCheck system water pressure/system
piping/expansion tank.
ƔCheck control settings.
ƔCheck ignition and flame rod (clean and
reposition).
ƔCheck wiring and connections.
ƔInspect flame (stable, uniform).
ƔInspect flame signal.
If combustion or performance indicate
need:
ƔFlush heat exchanger.
ƔRemove and clean air intake filter.
4.4 Protecting the Boiler from Freezing
CAUTION
Damage due to freezing is not covered by the Navien limited
warranty.
ƔFreezing damage is most likely to occur due to back drafting
caused by negative pressure in the building. This is not a
manufacturing defect, and therefore, Navien will not warrant
any damages due to freezing. The installer is responsible for
ensuring that there is sufficient make-up air to avoid such
a situation and the owner is responsible for ensuring that
protection against freezing is maintained.
ƔTo avoid freezing issues, we strongly recommend the use of
a direct vent exhaust and intake system.Your installer should
ensure that the exhaust vent pipe and the air intake pipe are
both connected directly from the collars on the top of the
boiler to the outdoors. This type of vent system minimizes
air movement within the boiler.
ƔThis boiler has an optional recirculation mode that is used for
freeze protection. This mode should prevent the boiler from
freezing, even if the intake air duct is not vented directly.
ƔThe boiler is designed for indoor installation only.
To ensure that the boiler does not freeze, follow these guidelines:
ƔDo not unplug the power supply cord, except for routine
maintenance. The boiler has a freeze protection function that
requires electricity. The freeze protection function will operate
regardless of whether or not the power is turned on or off, as
long as the electric supply is still connected.
ƔDo not close the gas valve, except for routine maintenance, as
this will limit additional freeze protection.
ƔIf the boiler will not be used for an extended period, drain
the boiler.
If the power or gas supplies must be disconnected for an
extended period, drain the boiler. Freezing damage may occur if
there is water remained in the boiler in cold weather.
Note ƔIf hot water will not flow and you suspect that the
boiler is frozen, contact an authorized technician or
licensed professional.
ƔThis boiler requires very little maintenance, however
a qualified technician should inspect the boiler at
the beginning of every heating season and/or when
there is a problem.

Maintaining the Boiler 15
Cleaning the Condensate Trap
1. Inspect the condensate drain line, condensate fittings, and
condensate trap.
2. Remove any sediment in the trap.
3. Fill with fresh water until the water begins to pour out of the
drain.
Checking all Piping for Leaks
Eliminate all system or boiler leaks. Continual fresh makeup water
will reduce boiler life. Minerals can build up in sections, reducing
heat transfer, overheating heat exchanger, and causing heat
exchanger failure. Leaking water may also cause severe property
damage.
1. Inspect all water and gas piping and verify to be leak free.
2. Look for signs of leaking lines and correct any problems found.
Checking the Flue Vent System and Air Piping
1. Visually inspect the entire flue gas venting system and air
piping for blockage, deterioration or leakage. Repair any
joints that show signs of leakage. Verify that air inlet pipe is
connected and properly sealed (if installed).
2. Verify that boiler vent discharge and air intake are clean and
free of obstructions.
WARNING
Failure to inspect for the above conditions and have them
repaired can result in severe personal injury or death.
WARNING
ƔFollow the service and maintenance procedures given
throughout this manual and in component literature
shipped with the boiler. Failure to perform the service and
maintenance could result in damage to the boiler or system.
ƔFailure to follow the directions in this manual and
component literature could result in severe personal injury,
death, or substantial property damage.
ƔThe boiler should be inspected annually only by a qualified
service technician. In addition, the maintenance and care
of the boiler must be performed to assure maximum boiler
efficiency and reliability. Failure to service and maintain the
boiler and system could result in equipment failure.
ƔElectrical shock hazard – Turn off power to the boiler
before any service operation on the boiler except as noted
otherwise in this instruction manual. Failure to turn off
electrical power could result in electrical shock, causing
severe personal injury or death.
Addressing the Reported Problems
Inspect any problems reported by the owner and correct before
proceeding.
Inspecting the Installation Area
1. Verify that boiler area is free of any combustible materials,
gasoline and other flammable vapors and liquids.
2. Verify that air intake area is free of any of the contaminants
listed in Installation & Operation Manual. If any of these are
present in the boiler intake air vicinity, they must be removed.
If they cannot be removed, reinstall the air and vent lines per
the Installation and Operation Manual.
Inspecting the Boiler Interior
1. Remove the front cover and inspect the interior of the boiler.
2. Vacuum any sediment from inside the boiler and components.
Remove any obstructions.

16 Maintaining the Boiler
Checking the Water System
1. Verify all system components are correctly installed and
operational.
2. Check the cold fill pressure for the system. Verify it is correct
(must be a minimum of 12 psi).
3. Watch the system pressure as the boiler heats up (during
testing) to ensure pressure does not rise too high.
Note
ƔIf the system contains glycol, test for proper
concentration as recommended by manufacturer.
ƔExcessive pressure rise indicates expansion tank
sizing or performance problem.
4. Inspect automatic air vents and air separators. Remove air vent
caps and briefly press push valve to flush vent.
5. Replace caps. Make sure vents do not leak. Replace any leaking
vents.
Checking Expansion Tank
ƔExpansion tanks provide space for water to move in and out as
the heating system water expands due to temperature increase
or contracts as the water cools.
ƔPerform annual checks as recommended by manufacturer to
ensure proper operation.
Checking the Pressure Relief Valves
1. Inspect the relief valve and lift the lever to verify flow. Before
operating any relief valve, ensure that it is piped with its
discharge in a safe area to avoid severe scald potential.
Note Safety relief valves should be inspected at least once
every three years, by a licensed plumbing contractor
or authorized inspection agency, to ensure that the
product has not been affected by corrosive water
conditions and to ensure that the valve and discharge
line have not been altered or tampered with illegally.
WARNING
ƔCertain naturally occurring conditions may corrode the
valve or its components over time, rendering the valve
inoperative. Such conditions are not detectable unless
the valve and its components are physically removed and
inspected. This inspection must only be conducted by a
plumbing contractor or authorized inspection agency – not
by the owner. Failure to re-inspect the boiler relief valve
as directed could result in unsafe pressure buildup, which
can result in severe personal injury, death, or substantial
property damage.
ƔFollowing installation, the valve lever must be operated at
least once a year to ensure that waterways are clear. Certain
naturally occurring mineral deposits may adhere to the valve,
rendering it inoperative. When manually operating the lever,
water will discharge and precautions must be taken to avoid
contact with hot water and to avoid water damage.
ƔBefore operating lever, check to see that a discharge line
is connected to this valve directing the flow of hot water
from the valve to a proper place of disposal. Otherwise
severe personal injury may result. If no water flows, valve is
inoperative. Shut down the boiler until a new relief valve has
been installed.
2. After following the above warning directions, if the relief
valve weeps or will not seat properly, replace the relief valve.
Ensure that the reason for relief valve weeping is the valve and
not over-pressurization of the system due to expansion tank
waterlogging or undersizing.
Inspecting the Ignition and Flame Detector Electrodes
1. Remove the ignition and flame detector electrodes from the
boiler heat exchanger.
2. Remove any deposits accumulated on the ignition/flame
detector electrode. If the electrodes cannot be cleaned
satisfactorily, replace with new ones.
3. Replace ignition/flame detector electrode, making sure gasket
is in good condition and correctly positioned.

Maintaining the Boiler 17
Checking the Ignition Ground Wiring
1. Check that the ground wire is in good condition and securely
attached to the boiler casing.
2. Check ground continuity of wiring using continuity meter.
3. Replace ground wires if ground continuity is not satisfactory.
Checking all Boiler Wiring
Inspect all boiler wiring, making sure wires are in good condition
and securely attached.
Checking the Control Settings
1. From the front panel, enter the Diagnostics Mode and check all
settings. Adjust settings if necessary.
2. Check settings of external limit controls (if any) and adjust if
necessary.
Performing Start-up and Checks
1. Start boiler and make sure that the boiler is operating properly.
2. Verify cold fill pressure is correct and that operating pressure
does not go too high.
Check the Burner Flame
1. Inspect flame through observation window.
2. If the flame is unsatisfactory at either high fire or low fire, check
for obstructions in the venting and ensure that the air intake
filter is clean.
Review with the Owner
1. Review the User’s Information Manual with the owner.
2. Emphasize the need to perform the maintenance schedule.
3. Remind the owner of the need to call a licensed contractor
should the boiler or system exhibit any unusual behavior.
4. Remind the owner to follow the proper shutdown procedure
and to schedule an annual start-up at the beginning of the
next heating season.
Flushing the Heat Exchanger
CAUTION
Flushing the heat exchanger is a somewhat complicated
procedure. Read the following instructions carefully before
attempting this procedure. If you are uncertain about any of
the steps in the procedure, contact an authorized technician or
licensed professional. Keep in mind that improper maintenance
can void your warranty.
Refer to the“2.2 Parts of the Boiler” on page 5 for details about
part locations.
Before flushing the Heat Exchanger, gather the following items:
ƔA bucket that is 5 gallons or larger
ƔCleaning solution diluted with water
Ɣ3 hoses
ƔA water circulation pump
Ɣ2 flush valves (if not installed)
Note Before flushing the heat exchanger, additional flush
valves (“A” and “B”) must be installed on the near boiler
piping (included with Navien Manifold System).
A
B
CD

18 Maintaining the Boiler
7. Pour the cleaning solution into the bucket.
8. Open both “A” and “B” valves.
9. Turn on the circulation pump and allow the solution to
circulate through the boiler. Refer to the manufacturer’s
literature for information about the circulation time.
10. Rinse the cleaning solution from the boiler:
a. Remove the free end of the drain tube from the bucket and
place it in the condensate drain or laundry tub (wherever
the boiler drains).
b. Close the “A” valve and open the“C” valve. Do not open the
“D” valve yet.
c. Allow water to flow through the boiler for 5 minutes.
d. Close the “B” valve and open the “D” valve.
11. Disconnect all tubes and valves.
12. Reconnect the power supply to the boiler.
13. Press the Power button on the front panel to turn on the boiler.
To flush the Heat Exchanger:
A
B
C
D
System Supply
System Return Circulation Pump
Flushing Kit
Navien Manifold
System
Pump in
Manifold System
1. Press the Power button on the front panel to turn off the boiler.
2. Disconnect the power supply to the boiler.
3. Close the “C” and “D”valves on the supply and return water
lines.
4. Connect one tube to the “B” valve and place the free end in the
bucket.
5. Connect one of the tubes to the circulation pump outlet and
the return water line at the“A”valve.
6. Connect one tube to the circulation pump inlet and place the
free end in the bucket.

Troubleshooting 19
MODE
If resetting the boiler and attempting the remedies suggested below do not resolve the problem, contact an authorized technician, a licensed
professional, or Technical Support at 1-800-519-8794 for service instructions.
Problem Possible Cause(s) What to do
Space heating side malfunction
Is the setting temperature too low?
Check the boiler’s temperature setting.
See “3.2 Adjusting the Temperature” on
page 8.
Is there power to the system, or is the system
in stand by?
Make sure the power is on, and plugged
into the outlet with the correct voltage.
Press the Power button and raise the setting
temperature. Make sure the boiler is turned
on.
Is the system running for domestic hot water
(DHW)?
When the unit is heating for DHW, the
heating side does not work.
5. Troubleshooting
5.1 Solving Basic Problems
If you experience a problem with the boiler, refer to the following
chart for possible remedies. Error codes that appear on the front
panel display are explained in the following section.
For minor problems, resetting the boiler may resolve the issue. To
reset the boiler, press the Reset button on the front panel.

20 Troubleshooting
5.2 Understanding Error Codes
When an error code appears on the front panel, refer to the following chart for a definition and possible remedy for the situation.
Error Code Reason Self-diagnostic/Action
E001 Heat exchanger over temperature Auto reset/Manual reset/Power On reset
E003 Ignition failure Manual reset/Power On reset
E004 False flame detection Auto reset
E012 Flame loss Manual reset/Power On reset
E016 Heat exchanger overheat Manual reset/Power On reset
E030 Abnormal operation: exhaust temperature Auto reset/Manual reset/Power On reset
E046 Abnormal operation: heat exchanger overheating sensor Auto reset
E047 Abnormal operation: exhaust thermostat Auto reset/Manual reset/Power On reset
E060 Abnormal operation: dual venturi Alarm
E109 Abnormal operation: fan motor Manual reset/Power On reset
E110 Exhaust vent closed Manual reset/Power On reset
E205 Abnormal operation: heating supply thermistor Auto reset
E218 Abnormal operation: heating return thermistor Alarm
E271 Temperature differential limit Alarm
E278 Abnormal operation: system supply thermistor Alarm
E279 Abnormal operation: system return thermistor Alarm
E291 Supply/Return inversion limit Manual reset/Power On reset
E302 Low water pressure Manual reset
E352 High water pressure Auto reset
E353 Abnormal operation: water pressure sensor Auto reset
E515 Abnormal operation: PCB component Alarm/Manual reset/Power On reset
E517 Abnormal operation: DIP switch setting (PCB) Manual reset/Power On reset
E594 Abnormal operation: EEPROM (PCB) Alarm
E615 Abnormal operation: MCU Alarm/Auto reset/Manual reset/Power On
reset
E740 Abnormal operation: outdoor temperature sensor Alarm
E777 Abnormal operation: LWCO limit (external device) Auto reset
E782 Abnormal operation: boiler communication Alarm
E784 Abnormal operation: zone controller communication (external device) Alarm
If these remedies do not resolve the problem, contact Technical Support at 1-800-519-8794.