Bosch 520-HN-N, 520-HN-L User Instructions
520 HN
Flow Modulated with Hydro-generated Ignition
Suitable for heating potable water only - Not approved for space heating purposes
(Intended for variable flow applications with steady cold water inlet temperatures)
520-HN-N
520-HN-L
6 720 644 942 (2010/09) US
Warning: If the information in this manual 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
vapor and liquids in the vicinity of this or any other
appliance.
Improper installation, adjustment, alteration,
service or maintenance can cause injury or
property damage. Refer to this manual. For
assistance or additional information consult a
qualified installer, service agency or the gas
supplier.
In the Commonwealth of Massachusetts this
product must be installed by a licensed plumber or
gas fitter.
Upon completion of the installation, these
instructions should be handed to the user of the
appliance for future reference.
What to do if you smell gas
• Close gas valve. Open windows.
• Do not try to light any appliance.
• Do not touch any electrical switch; do not use any
phone in your building.
• Immediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
• 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.
6 720 644 942
2
Index
Index
1 Warning 2
2 Appliance details 3
2.1 520 HN specifications (Technical data) 3
2.2 Unpacking the 520 HN heater 4
2.3 General rules to follow for safe operation 4
2.4 Dimensions and installation clearances 5
3 Installation instructions 6
3.1 Introduction 6
3.2 Proper location for installing your heater 6
3.3 Venting 6
3.4 Combustion air requirements 9
3.5 Mounting Heater 9
3.6 Gas piping & connections 11
3.7 Measuring gas pressure 13
3.8 Water connections 13
3.9 Recirculation application 14
4 Operation instructions 14
4.1 For your safety, read before operating your water heater 14
4.2 Lighting instructions 15
4.3 To turn off appliance 15
4.4 Adjusting the water temperature 15
4.5 Power adjustment knob 16
4.6 Draining the appliance 16
5 Maintenance and service 17
5.1 Maintenance intervals 17
5.2 Water valve 17
5.3 Pilot 17
5.4 Main burners 18
5.5 Vent assembly 18
5.6 Mineral scale build-up 18
6 Troubleshooting 19
6.1 Introduction 19
6.2 No spark at pilot with water flow 19
6.3 Spark appears when hot water is turned on,
but pilot and burners will not ignite 19
6.4 Pilot lights, but burners will not come on. 20
6.5 Main burners go out during hot water use 20
6.6 Hot water temperature fluctuates at tap 21
6.7 Water is too hot 21
6.8 Water is not hot enough 22
6.9 Low hot water pressure 22
6.10 Noise when heater is running 22
6.11 Burners do not burn cleanly, yellow
flames when operating 22
7 Protecting the environment 23
8 Interior components and diagram parts list 24
8.1 Interior components 24
8.2 Components diagram 25
8.3 Parts list 26
9 Fifteen Year Limited Warranty 27
1 Warning
Fig. 1
Warning: The heater must be isolated
from the gas supply piping system
during any pressure testing of that
system at test pressures equal to or
more than 0.5 psig.
Caution: Any changes or
modifications not expressly approved
by the party responsible for compliance
could void the user’s authority to
operate the equipment.
HOT
BURN
D A N G E R
Watertemperatureover125°Fcan
causesevereburnsinstantlyor
deathfromscalds.
Children,disabledandelderlyare
athighestriskofbeingscalded.
Seeinstructionmanualbefore
settingtemperatureatwater
heater.
Feelwaterbeforebathingor
showering.
6720608643-16.1AL
6 720 644 942
Appliance details
3
2 Appliance details
2.1 520 HN specifications (Technical
data)
Approved in US/Canada
Capacity
520 HN: 4.36 GPM
Minimum input
520 HN: 30,735 Btu/hr
Maximum input
520 HN: 117 000 Btu/hr
Min. Output
520 HN: 23 906 Btu/hr
Maximum output
520 HN: 91 525 Btu/hr
Efficiency in %
Efficiency 80%
Gas Requirement
Gas connection - ¾” NPT
Inlet gas pressure under maximum operation:*
• Propane: 10.5” - 14” water column
• Natural Gas: 5.7” - 14” water column.
* To measure Gas Pressure, see Measuring Gas
Pressure, chapter 3.7.
Venting
• Natural Draft
• Vent diameter - 5" or 6"
• Minimum height (feet) - 6’ with no elbows
• Vertical termination through roof or into chimney.
• Sidewall termination only with AQ4 power vent kit.
Water
• Hot water connection - ½” NPT
• Cold water connection - ½” NPT
• Water valve material: Fiberglass reinforced polymide
(PA)
• Minimum water flow to activate heater: 0.5 gallon/
minute (1.9 l/m)
• Minimum recommended water pressure: 30 PSI
(2.07 bar)
• Connections:
– Bottom of heater
• Temperature rises:
1)
– 45F rise @ 4.1 gpm
– 50F rise @ 3.7 gpm
– 55F rise @ 3.4 gpm
– 65F rise @ 2.8 gpm
– 77F rise @ 2.4 gpm
– 90F rise @ 2.0 gpm
Dimensions
• Depth (in): 8.66” (220 mm)
• Width (in): 16.73” (425 mm)
• Height (in): 25.75” (655 mm)
• Weight: 35 pounds (16 kg).
Gas types
Natural Gas
LP Gas
Safety devices
• Flame failure device (ionization flame rod)
• Pressure relief valve (Available as accessory)
• Overheat prevention (temperature limiter).
Water protection
IP X4.
Accessories (Bosch part #)
• Freeze prevention kit (7709003775)
2)
• Pressure relief valve (FWL-2).
1) Depending on gas pressure and altitude.
2) The freeze prevention kit is designed to provide protection for the water heater down to approximately 5°F for
short term conditions only. It will not protect the appliance in areas where the temperature is routinely
expected to be below freezing.
- The freeze prevention kit will not protect plumbing outside the appliance from freezing. Precautions should be
taken.
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Appliance details
2.2 Unpacking the 520 HN heater
Before installing the unit, be certain you have the
correct heater for your type of Gas - Propane or
Natural Gas. Identification labels are found on the
shipping box, and on the rating plate which is located on
the right side panel of the cover.
B Installer must fill out checklist on back cover to
provide details in case service or warranty coverage is required.
Fig. 2 Rating plate
A Serial number
B Type of gas
The box includes:
• Hot and cold water connection fittings
• Mounting screws
• Product registration card
• Installation manual
• Incandescent particle tray.
Do not lose this manual, there is a charge for a
replacement.
Please complete and return the enclosed product
registration card.
The 520 HN is not approved or designed for:
• Manufactured (mobile) homes, RV's or boats
• Heating or other recirculating/pumping applications*
• Solar/preheat backup or high temperature booster
use
• Installation in bathroom, bedroom or other occupied
rooms normally kept closed.
* This includes domestic hot water circulator pump loop
systems that may be installed in home hot water system
prior to installing this unit. An approved recirculation
design can be found in chapter 3.9.
2.3 General rules to follow for safe
operation
1. You must follow these instructions when you install
your heater. In the United States: The installation must
conform with local codes or, in the absence of local
codes, the National Fuel Gas Code ANSI Z223.1/
NFPA 54.
In Canada: The Installation must conform with CGA
B149.(1,2) INSTALLATION CODES and /or local
installation codes.
2. Carefully plan where to install the heater. Proper
clearances must be followed.
3. The appliance must be isolated from the gas supply
piping system by closing its individual manual gas
shutoff valve (not supplied with heater) during any
pressure testing in excess of ½ Psig (3.5 kPa).
The appliance and its gas connection must be leak
tested before placing the appliance in operation.
4. Keep water heater area clear and free from
combustibles and flammable liquids. Do not locate the
heater over any material which might burn.
5. Correct gas pressure is critical for the optimum
operation of this heater. Gas piping must be sized to
provide the required pressure at the maximum output of
the heater, while all the other gas appliances are in
operation. Check with your local gas supplier, and see
chapter 3.6 and 3.7 to verify proper gas line sizing.
6. Should overheating occur or the gas supply fail to
shut off, turn off the gas supply at the manual gas shut
off valve, on the gas line. Note: manual gas shutoff valve
is not supplied with the heater.
7. Do not use this appliance if any part has been
underwater. 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 underwater.
i
BOSCH is constantly improving its
products, therefore specifications are
subject to change without prior notice.
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Appliance details
5
2.4 Dimensions and installation clearances
Fig. 3 Dimensions in Inches and (mm)
4 Heat exchanger
5 Burner
10 Flow control knob
11 Water valve
20 Gas connection
23 Ignition unit
26 Power adjustment knob
34 LED indicator for burner status
35 On/Off switch
36 Front cover
37 Mounting holes
38 Exhaust pipe union
39 Draft diverter with flue gas sensor
40 Gas valve
Fig. 4 Minimum clearances
39
38
4
5
23
11
40
H
6720608036-01.2Av
8,66"(220)
E
F
G
4,92"(125)
D
2,50"
(63.5)
1,97"
(50)
3,82"
(97)
A
B
37
10
26
35
34
20
36
C
Model 520 HN
TOP (A)
12 inches (306 mm)
FRONT (B)
4 inches (100 mm)
BACK
0 inches
SIDES
4 inches (100 mm)
BOTTOM (C)
12 inches (306 mm)
Dimensions inches (mm)
520 HN
A 16.73” (425)
B 25.75” (655)
C 13.15” (334)
D 5.11” (130)
E 21.25” (540)
F 2.55” (65)
G 1.18” (30)
H 3/4”
Table 1 Dimensions in inches (mm)
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Installation instructions
3 Installation instructions
3.1 Introduction
Please follow these instructions. Failure to follow
instructions may result in:
B Damage or injury.
B Improper operation.
B Loss of warranty.
If you are unable to perform the tasks required to install
this heater properly, please contact a locally licensed
plumber or gas technician.
Please contact Bosch Water Heating with any
questions.
3.2 Proper location for installing your
heater
Carefully select the location of the water heater. For
your safety and for proper heater operation, you must
provide combustion air to the heater and a proper
exhaust vent system.
Follow the guidelines below:
B 1. Common installation practice is to determine the
venting system layout and penetration first, then work
back to the heater.
B 2. Locate the heater where venting, gas and plumb-
ing connections are feasible and convenient.
B 3. The hot water lines should be kept short to save
energy. Centrally locating the water heater is best. It
is always best to have hot water lines insulated.
3.3 Venting
B Minimum vent pipe diameter: 5 inches
B Minimum vertical vent height: 6 feet, with no elbows
B Establish 12 inch rise before any elbow
The heater must be vented to the outside following all
local ordinances and specifications for installing a gas
appliance vent or chimney. The heater must be located
as close as practicable to a vertically rising chimney or
vent that has a listed vent cap at its termination point.
The venting system must be designed and constructed
so as to develop a positive flow adequate to remove flue
gasses to the outdoors. Consult the National Fuel Gas
Code if the vent will have elbows or share venting with
another natural draft appliance.
3.3.1 Horizontal venting
An AQ4 powervent, with a proof-of-draft safety interlock
device, is required and is available for sidewall venting.
Contact your dealer. In the Commonwealth of
Massachusetts power vented applications must utilize
proof-of-draft safety interlock device and comply with
regulations established for all side wall horizontally
vented gas fueled equipment.
3.3.2 Vertical venting
B A 5 inch diameter gas vent constructed of double
wall Type B gas vent is recommended. A 6 inch vent
is required in elevations greater than 2000 feet, see
Fig. 10. Under no circumstances must the vent pipe
be reduced in size.
Warning: The water in this water
heater is cold and always remains cold
except for the times that hot water is
being used. DO NOT INSTALL IN AN
AREA WHERE IT COULD FREEZE.
Drain the heater entirely if freezing
temperatures are anticipated in area
where heater is installed. See chapter
4.6 for draining instructions.
To prevent any freeze damage,
introduce short bursts of compressed
air (20-40psi) through these
connections to remove the residual
water in the horizontal pipes and water
valve.
Warning: Flammable materials,
gasoline, pressurized containers, or any
other items or articles that are potential
fire hazards must NOT be placed on or
adjacent to the heater. The appliance
area must be kept free of all
combustible materials, gasoline and
other flammable vapors and liquids.
Warning: Place the heater in a location
where water leaks will do NO DAMAGE
to adjacent areas.
Danger: Do not reduce the vent pipe
size. Do not put an elbow directly on top
of heater. Failure to follow venting
requirements may result in dangerous
exhaust gases entering living space.
Warning: Do not combination vent with
a power vented appliance.
Warning: Horizontally venting to a
vertically constructed vent stack along
an outside wall of a building is not
permissible.
Warning: Horizontally venting to a
sidewall vent terminator (without
powervent) is not permissible.
6 720 644 942
Installation instructions
7
B An approved gas vent connector must be attached to
the top of the water heater and rise vertically at least
12" before entering into an approved gas vent
connector elbow.
B The minimum vertical gas vent height allowed is 6
feet; horizontal vent connectors and elbows are not
to be considered in the total gas vent height.
B All gas vent sections must be secured to each other
with sheet metal screws and be properly supported.
Horizontal runs:
Any gas vent section that is greater than 45 degrees
from the vertical is considered horizontal. Horizontal
sections must slope upwards at least ¼ inch for every
foot of its horizontal length and be properly supported.
Keep the horizontal section short and avoid too many
elbows. The maximum horizontal run allowed is half of
the total vertical vent height; horizontal vent connectors
and elbows are not to be considered in the total gas
vent height.
Vent termination:
The gas vent constructed of double wall Type B gas
vent must terminate above the roof surface with a listed
vent cap at a height that's in accordance with Fig. 7 and
table 2, provided they are at least 8 feet (2.4 m) from a
vertical wall or similar obstruction. All other gas vents
that are not able to terminate within the minimum
specified height allowed must terminate not less than 2
feet (0.6 m) above the highest point where it passes
through the roof and at least 2 feet (0.6 m) higher than
any vertical wall or similar obstruction within 10 feet (3.1
m).
Fig. 5 Flat roof
Fig. 6 Vent Adaptor for High Altitude Installations
Freeze prevention
In cold climates, components of a tankless water heater
can freeze and burst from negative draft. A leading
cause of negative draft is combustion appliances in the
building not being supplied with sufficient combustion
air. A wood stove or furnace can pull its combustion air
from the water heater‘s vent pipe, allowing the cold
incoming air to freeze the cold water in the heat
exchanger. Supplying more combustion air for all combustion appliances is the solution. A HVAC specialist
should be consulted to design solutions for providing
more combustion air.
In cold climates where backdraft is a problem,
the freeze prevention kit accessory (7709003775)
should be installed.
LISTED VENT CAP
MINIMUM 6
FEET (1.8M)
LISTED GAS VENT
ESTABLISH A ONE
FOOT RISE BEFORE
ANY ELBOWS
5” X 6” ADAPTOR
USED AT HIGH
ALTITUDE
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Installation instructions
Masonry chimney
Masonry chimneys shall be built and installed in
accordance with NFPS 211 or local codes. A minimum
5" diameter gas vent pipe (metal double wall Type B),
or an approved clay flue liner or a listed chimney lining
system must be used when venting into a naturally
drafting, internal masonry chimney. 6 inch is required in
elevations greater than 2000 feet, see Fig. 6. Local
codes may require the use of both gas vent and an
approved lining system when venting into a masonry
chimney. The Commonwealth of Massachusetts
requires the use of a listed liner. Lining systems include
approved clay flue lining, a listed chimney lining system
or other approved material that will resist corrosion,
erosion, softening, or cracking from exhaust flue gases
at temperatures up to 1800 degrees F. The lining
system must be listed for use with naturally drafting,
draft hood equipped gas appliances. Follow local
codes and refer to NFGC 54 and NFPA 58.
Existing interior masonry chimney
The metal gas vent pipe should be permanently
mounted inside the masonry chimney. Double wall Type
B gas vent is recommended. The masonry chimney may
have to be tile or metal lined before the insertion of the
gas vent pipe; check local codes for clarification. The
lining material must be listed for use only with naturally
drafting, draft hood equipped gas appliances. Follow
manufacturer's instructions for installation of listed
lining material. You may not vent any other fuel burning
appliances into any free space remaining in the
chimney. The minimum vertical gas vent length within
the masonry chimney must be no less than 5 ft (1.5 m);
the vent terminator must extend at least 3 feet (0.9 m)
above where the chimney meets the roofline and at least
2 feet (0.6 m) higher than any vertical wall or similar
obstruction within 10 feet (3.1 m). The top of the gas
vent must have an approved vent terminator. See Fig. 8.
Fig. 7 Pitch roof
Fig. 8 Masonry chimney
APPROVED VENT CAP
LOWEST DISCHARGE
OPENING
MINIMUM 6
FEET (1.8M)
X
12
ROOF
PITCH IS
X/12
LISTED GAS VENT
H (minimum) height
from roof to lowest
discharge opening
ESTABLISH A ONE
FOOT RISE BEFORE
ANY ELBOWS
GAS VENT TERMINATIONS FOR LISTED VENT CAPS
Roof pitch H (minimum) feet meters
Flat to 6/12 1.0 0.30
6/12 to 7/12 1.25 0.38
Over 7/12 to 8/12 1.5 0.46
Over 8/12 to 9/12 2.0 0.61
Over 9/12 to 10/12 2.5 0.76
Over 10/12 to 11/12 3.25 0.99
Over 11/12 to 12/12 4.0 1.22
Over 12/12 to 14/12 5.0 1.52
Over 14/12 to 16/12 6.0 1.83
Over 16/12 to 18/12 7.0 2.13
Over 18/12 to 20/12 7.5 2.27
Over 20/12 to 21/12 8.0 2.44
Table 2
6720608032-14.1Av
GAS
VENT
APPROVED
VENT CAP
VENT
CONNECTOR
Establish a
one foot
rise before
any elbows
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Installation instructions
9
3.4 Combustion air requirements
The Protankless water heater holds cold water in its
copper heat exchanger and water valve when not in use.
Because of this, any cold air that comes down through
the unit's vent pipe is capable of freezing these
components. This Installation Manual specifies the
minimum vertical vent pipe and the amount of
combustion air required for this unit. When all
requirements are followed, the unit will operate properly
and safely. However, there may still be a risk of freezing
due to negative draft if all the combustion appliances in
the structure are not being supplied with sufficient
combustion air. A wood stove or furnace can pull it's
combustion air from the Protankless vent pipe. This
allows the cold infiltrating air to potentially freeze the
cold water in the AquaStar heater. Damage from
freezing is not covered under the manufacturer's
warranty. Supplying more combustion air for all
combustion appliances is the solution. Follow the
instructions on venting and checking adequacy of
combustion air. A HVAC specialist should be consulted
to design solutions for providing more make-up air if
necessary. Observe the following instructions
concerning combustion air.
Appliances located in unconfined spaces:
a) An unconfined space is one whose volume is greater
than 50 cubic feet per 1000 Btu per hour of the
combined rating of all appliances installed in the space.
That would be 5850 cubic feet for the Protankless 520
HN alone.
b) Installations in structures that have been tightly
constructed (air infiltration rate of 0.40 ACH or less)
must be provided with combustion air per the National
Fuel Gas Code. Consult a HVAC specialist if your air
infiltration rate is questionable.
Appliances located in confined spaces:
The confined space must be provided with two
permanent openings, one commencing within 12
inches of the top and one commencing within 12 inches
of the bottom of the enclosure. Each opening must have
a minimum free area of one square inch per:
• 1000 Btu/hr if all air is taken from inside the building.
• 2000 Btu/hr if all air is taken from the outside by
horizontal ducts.
• 4000 Btu/hr if all air is taken from the outside by
direct openings or vertical ducts.
Or the confined space must be provided with one
permanent opening or duct that is within 12 inches of
the ceiling of the enclosure. This opening must have a
minimum free area of one square inch per:
• 3000 Btu/hr if all air is taken from the outside by a
direct opening or vertical duct.
Louvers, grills and screens have a blocking effect. If the
effective free area is not known, increase the sizes of
your openings by 400% if your louvers are wood and by
135% if your louvers are metal. Refer to the National
Fuel Gas Code for complete information. In buildings of
tight construction all air should be taken from outside.
3.5 Mounting Heater
The 520 HN is approved for installation on a combustible wall provided the floor covering below the heater is
noncombustible. For installations in an alcove or closet,
maintain the minimum clearances to combustible and
non-combustible materials listed in Fig. 4.
Remove cover and inspect.
B Remove the flow control and power adjustment
knobs.
B Unsrew the cover fixing screws, see Fig. 10.
B Loosen the two Phillips head screws located on
bottom rear of cover. Remove cover by pulling it
outward and then lifting upwards.
B Ensure that the flue terminal is clear.
B After inspection, replace front cover and tighten
screws.
Install incandescent particle tray.
B Install incandenscent particle tray using screws
provided as shown in Fig. 9.
Fig. 9 Incandescent particle tray illustration
Warning: before starting installation:
B check that there are no loose parts
inside the appliance
B ensure that gas pipe, gas valve, and
burner have no damage and are
properly fitted.
B Read chapter 2.2 to verify proper gas
type and to verify all parts are included
in box.
i
Front cover must be removed in order to
inspect components visually (see
instructions below).
Incandescent particle tray
Screws
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