Bosch 520-HN -L User manual

INDOOR MODEL Flow Modulated with Hydro-generated Ignition
520 HN
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.
520-HN-N / 520-HN -L
6 720 644 942 (2014/11) US
Suitable for heating potable water only - Not approved for space heating purposes
(Intended for variable flow applications with steady cold water inlet temperatures)

6 720 644 942 (2014/11) 520 HN
2 | Index
Index
1 Key to symbols and safety instructions . . . . . . . . . . . . 3
1.1 Key to symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 General safety instructions . . . . . . . . . . . . . . . . . . . 3
2 Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Appliance details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 520 HN specifications (Technical data) . . . . . . . . 7
3.2 Unpacking the 520 HN heater . . . . . . . . . . . . . . . . 8
3.3 General rules to follow for safe operation . . . . . . . 8
3.4 Dimensions and installation clearances . . . . . . . . 10
4 Installation instructions . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2 Proper location for installing your heater . . . . . . 11
4.3 Mounting Heater . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4 Combustion air requirements . . . . . . . . . . . . . . . . 13
4.5 Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.5.1Horizontal venting . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.5.2Vertical venting . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.6 Gas piping & connections . . . . . . . . . . . . . . . . . . . 16
4.7 Measuring gas pressure . . . . . . . . . . . . . . . . . . . . 20
4.8 Water connections. . . . . . . . . . . . . . . . . . . . . . . . 20
4.9 Recirculation application . . . . . . . . . . . . . . . . . . . 21
5 Operation instructions . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1 For your safety read before operating
your water heater . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2 Lighting instructions . . . . . . . . . . . . . . . . . . . . . . . 21
5.3 To turn off appliance . . . . . . . . . . . . . . . . . . . . . . . 22
5.4 Adjusting the water temperature . . . . . . . . . . . . . 22
5.5 Power adjustment knob . . . . . . . . . . . . . . . . . . . . 23
5.6 Draining the appliance . . . . . . . . . . . . . . . . . . . . . 23
6 Maintenance and service . . . . . . . . . . . . . . . . . . . . . . . 24
6.1 Maintenance intervals . . . . . . . . . . . . . . . . . . . . . . 24
6.2 Water valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.3 Pilot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.4 Main burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.5 Vent assembly / heat exchanger . . . . . . . . . . . . . . 25
6.6 Mineral scale build-up . . . . . . . . . . . . . . . . . . . . . . 25
6.6.1Descaling heat exchanger . . . . . . . . . . . . . . . . . . . 25
7 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.2 No spark at pilot with water flow . . . . . . . . . . . . . 26
7.3 Spark appears when hot water is turned on,
but pilot and burners will not ignite . . . . . . . . . . . 26
7.4 Pilot lights, but burners will not come on . . . . . . 27
7.5 Main burners go out during hot water use . . . . . . 28
7.6 Hot water temperature fluctuates at tap . . . . . . . 28
7.7 Water is too hot . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.8 Water is not hot enough . . . . . . . . . . . . . . . . . . . . 29
7.9 Burners ignite without hot water flow . . . . . . . . . 29
7.10 Low hot water pressure . . . . . . . . . . . . . . . . . . . . 29
7.11 Noise when heater is running . . . . . . . . . . . . . . . . 30
7.12 Burners do not operate cleanly; yellow flames
when operating . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
8 Protecting the environment . . . . . . . . . . . . . . . . . . . . 30
9 Interior components and diagram parts list . . . . . . . 31
9.1 Interior components . . . . . . . . . . . . . . . . . . . . . . . 31
9.2 Components diagram . . . . . . . . . . . . . . . . . . . . . . 32
9.3 Parts list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10 LIFETIME LIMITED WARRANTY FOR BOSCH TANKLESS
WATER HEATERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
11 Installer Checklist to be completed by installer upon
installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

6 720 644 942 (2014/11)520 HN
Key to symbols and safety instructions | 3
1 Key to symbols and safety instructions
1.1 Key to symbols
Warnings
The following keywords are defined and can be used in this
document:
•DANGER indicates a hazardous situation which, if not
avoided, will result in death or serious injury.
•WARNING indicates a hazardous situation which, if not
avoided, could result in death or serious injury.
•CAUTION indicates a hazardous situation which, if not
avoided, could result in minor to moderate injury.
•NOTICE is used to address practices not related to
personal injury.
Important information
Additional symbols
1.2 General safety instructions
Read all instructions before installing. Perform the steps in the
indicated sequence. Have the water heater inspected by a
trained service technician at least once every year. Failure to
comply with these instructions can result in severe, possibly
fatal, personal injury as well as damage to property and
equipment.
Installation and servicing
▶Risk of fire when soldering and brazing!
Take appropriate protective measures when soldering and
brazing around combustible and flammable material.
▶ Ensure that only a licensed contractor installs or services
the water heater.
▶ On hot components use only material with adequate
temperature stability.
Installation and commissioning
▶ In the Commonwealth of Massachusetts, the water heater
must be installed by a licensed plumber.
▶ Do not install this device in rooms with a high moisture level
(e.g. bathrooms, saunas).
Function
▶ To ensure that the water heater functions properly, follow
these installation and maintenance instructions.
▶ Never close the blow-off line of the T&P safety valve. For
safety reasons, water may escape during heating.
If you smell gas
▶ Turn off the gas shut-off valve.
▶ Open windows and doors.
▶ Do not try to light the appliance.
▶ Do not touch any electrical switch, telephone, and do not
use outlets.
▶ Extinguish all open flames. Do not smoke! Do not use
lighters!
▶ Warn all occupants of the building. Do not ring doorbells!
▶ If you can hear gas leaking, leave the building immediately.
▶ Prevent others from entering the building and notify the
police and fire department from outside the building.
▶ From outside the building, call the gas utility company and
a trained and certified installer.
If you smell flue gas
▶ Switch off the appliance.
▶ Open windows and doors.
▶ Inform a trained and certified installer.
Insufficient ventilation may cause toxic flue gas to escape.
Risk of poisoning.
▶ Never close off or reduce the size of the air intake and outlet
openings.
▶ The appliance must not be operated until any obstructions
have been removed.
▶ Inform the system operator in writing of the problem and
the associated dangers.
Warnings in this document are identified by
a warning triangle printed against a grey
background.
Keywords at the start of a warning indicate
the type and seriousness of the ensuing risk
if measures to prevent the risk are not taken.
This symbol indicates important information
where there is no risk to people or property.
Symbol Explanation
▶ Step in an action sequence
Cross-reference to another part of the document
• List entry
– List entry (second level)
Table 1

6 720 644 942 (2014/11) 520 HN
4 | Key to symbols and safety instructions
Danger from escaping flue gases
▶ Ensure all vent pipes and chimneys are not damaged or
blocked.
▶ Connect only one appliance to each vent system or
chimney liner.
▶ The venting system piping must not feed into another air
extraction duct.
▶ Do not route the flue system piping through or inside
another air extraction duct.
Danger of explosion of flammable gases
▶ Work on gas components may only be carried out by a
trained and certified installer.
▶ Installation,gasandflueconnection,initialcommissioning,
electrical connections and annual maintenance must only
be carried out by a trained and certified installer.
Combustion air
▶ Keep the combustion air free of corrosive substances
(halogenated hydrocarbons that contain chlorine or
fluorine compounds).
Never shut off safety valves!
▶ Water may escape from the safety valve at any time when
the water is being heated.
inspection/maintenance
▶ servicing and repairs may only be carried out by a trained
and certified installer.
▶ immediately correct all faults to prevent system damage.
▶ use only bosch spare parts! damage caused by the use of
parts not supplied by bosch may void the warranty.
instruct the customer
▶ explain to the customer how the appliance works and how
to operate it.
▶ inform the customer that he/she must not carry out any
alterations or repairs.
Danger from electric shock
▶ Ensure that only an authorized contractor performs
electrical work.
▶ Before performing electrical work, disconnect the power
and secure the unit against unintentional reconnection.
▶ Ensure the system has been disconnected from the power
supply.
Risk of scalding at the hot water draw-off point
▶ When the water heater is in operation, temperatures in
excess of 122 °F (50 °C) can occur. To limit the
temperature at the tap, install a thermostatic DHW mixing
valve.
▶ Water heated for washing the laundry, dishes and for other
cleaning purposes can cause scalding and permanent
injuries.
▶ Children, elderly, and handicapped persons are more likely
to be permanently injured by hot water. Never leave such
individuals in the tub or shower unattended under any
circumstances. Children must not be allowed to operate
hot water faucets themselves or to fill a bathtub.
▶ If the building has occupants in the above groups who
operate hot water faucets, or state laws / local ordinances
stipulate specific water temperatures, take the following
precautions:
– Use the lowest possible temperature setting.
– To prevent scalding, install a tempering device, such as
an automatic mixing valve, at hot water tap or water
heater. Select and install the automatic mixing valve in
accordance with the valve manufacturer's
recommendations and instructions.
▶ Water exiting from drain valves can be extremely hot. To
avoid injuries:
– Check that all connections are tight.
– Direct exiting water away from people.
▶ Measures must be taken to protect against excessive
temperature and pressure! Installation of a T&P safety
valve is required.
To protect against corrosion and ensure compliance with the
rules for electrical safety, observe the following points:
▶ Use metal fittings for potable water heating systems with
plastic piping.
▶ Use only original accessories from the manufacturer.
▶ When installation of the water heater is complete, inspect
the ground conductor (including metal fittings).
Maintenance
Customers are advised to:
▶ Sign a maintenance and inspection contract with an
authorized contractor. Inspect and maintain the water
heater as necessary and on a yearly basis. Service as
needed.
▶ Use only genuine spare parts.

6 720 644 942 (2014/11)520 HN
Key to symbols and safety instructions | 5
Flooding
▶ After a flood, do not use the appliance if any part has been
submerged. Damage to appliances that have been
submerged can be quite severe and pose numerous safety
risks.
▶ Every appliance that has been submerged must be
replaced.
For your safety
▶ Do not store or use gasoline or other flammable,
combustible or corrosive vapors and liquids in the vicinity
of this or any other appliance.
DANGER: Fatal accidents!
Carbon monoxide poisoning.
▶ Carefully plan where you install the
heater. Correct combustion air supply
and flue pipe installation are very
important. If a gas appliance is not
installed correctly, fatal accidents can
result such as carbon monoxide
poisoning or fire.
DANGER:
Carbon monoxide poisoning.
▶ Exhaust gas must be vented to outside
using approved vent material. See
table 5, page 16(In Canada use only
ULCS636 approved material). Vent and
combustion air connector piping must
be sealed gas-tight to prevent flue gas
spillage, carbon monoxide emissions
and risk of fire, resulting in severe
personal injury or death. Approved vent
terminations must be used when
penetrating to the outside.
DANGER: Electric shock!
▶ Field wiring connections and electrical
grounding must comply with local
codes, or in the absence of local codes,
with the latest edition of the National
Electric Code, ANSI/NFPA 70, or in
Canada, all electrical wiring must
comply with the local codes and the
Canadian Electrical Code, CSA C22.1
Part 1.
DANGER: Electric shock!
Shock hazard: line voltage is present.
▶ Before servicing the water heater,
unplug power supply cord from outlet.
Failure to do so could result in severe
personal injury or death.
WARNING: Damage to the appliance from
over pressure.
▶ The heater must be disconnected from
the gas supply piping system during
any pressure testing of that system at
test pressures equal to or more than
0.5 psi.
NOTICE:
▶ The appliance should be located in an
area where leakage of the heater or
connections will not result in damage to
the area adjacent to the appliance or to
lower floors of the structure. When such
locations cannot be avoided, it is
recommendedthata suitable drain pan,
adequately drained, be installed under
the appliance. The pan must not restrict
combustion air flow.
WARNING:
▶ The maximum inlet gas pressure must
not exceed the value specified by the
manufacturer and the minimum value
listed is for the purpose of input
adjustment.
NOTICE:
▶ If a water heater is installed in a closed
water supply system, such as one
having a backflow preventer in the cold
water supply line, means shall be
provided to control thermal expansion.
Contact the water supplier or local
plumbing inspector on how to control
this situation.

6 720 644 942 (2014/11) 520 HN
6 | Warning
2 Warning
WARNING: Fire danger!
▶ Keep appliance area clear and free from
combustible materials, gasoline and
other flammable vapors and liquids.
NOTICE:
▶ Do not obstruct the flow of combustion
and ventilation air.
NOTICE: Appliance malfunction!
▶ If power is lost while appliance is
operating. Turn off both water and
power for 15 seconds to reset device.
WARNING: Risk of scalding and property
damage.
▶ Precautions must be taken prior to
manually operating the relief valve to
avoid contact with hot water discharged
from the relief valve and to prevent
water damage.
NOTICE: Appliance damage!
▶ Label all wires prior to disconnection
when servicing controls. Wiring errors
can result in improper and dangerous
operation. Verify proper operation after
servicing.
WARNING: System damage!
▶ If a relief valve discharges periodically,
this may be due to thermal expansion in
a closed water supply system. Contact
the water supplier or local plumbing
inspector on how to correct this
situation. Do not plug the relief valve.
WARNING: Property damage!
▶ If the water heater is used in a space
heating application, all piping and
components connected to the water
heater must be suitable for use with
potable water.
WARNING: Personal Injury from toxic
chemicals.
▶ Toxic chemicals, such as those used for
boiler treatment, shall not be
introduced into the potable water used
for space heating.
WARNING: Personal Injury from toxic
chemicals.
▶ A water heater which will be used to
supply potable water shall not be
connected to any heating system or
component(s) previously used with a
nonpotable water heating appliance.
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.

6 720 644 942 (2014/11)520 HN
Appliance details | 7
Fig. 1
3 Appliance details
3.1 520 HN specifications (Technical data)
Approved in US/Canada
Capacity
520 HN: 4.36 GPM
Accessories (Bosch part #)
• Freeze prevention kit (7709003775)1)
• Pressure relief valve (FWL-2)
Water protection
• IP X4.
Safety devices
Flame failure device (ionization flame rod)
Pressure relief valve (Available as accessory)
Overheat prevention (temperature limiter).
1) 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.
Capacity
Minimum input BTU/hr 30 735 Btu/hr
Maximum input BTU/hr 117 000 Btu/hr
Minimum output BTU/hr 23 906 Btu/hr
Maximum output BTU/hr 91 525 Btu/hr
Thermal efficiency
(Efficiency in %)
% 80%
Gas Requirement
Gas connection inches ¾” NPT
Inlet gas pressure under maximum operation:*
Propane water
column
10.5” - 14”
* To measure Gas Pressure, see Measuring Gas Pressure,
chapter 3.7.
Natural Gas water
column
5.7” - 14”
Water
Hot water connection inches ½ ” NPT
Cold water connection inches ½ ” NPT
Minimum water flow GPM (l/
min)
0.5 (1.9)
Minimum recommended
water pressure
PSI (bar) 30 PSI (2.07 bar)
Water valve material Fibreglass -
reinforced
polyamide (PA)
Temperatures rises: 1)
Table 2

6 720 644 942 (2014/11) 520 HN
8 | Appliance details
3.2 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.
▶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 520HN 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 a bathroom 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 4.9.
3.3 General rules to follow for safe operation
1. You should 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 should conform with CGA
B149.(1,2) INSTALLATION CODES and /or local installation
codes.
2. Carefully plan where you install the heater. Proper
clearances must be followed.
- 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
Connections: Bottom of heater
Dimensions
Depth inches 8.66” (220 mm)
Width inches 16.73” (425 mm)
Height inches 25.75” (655 mm)
Weight pounds (kg) 35 pounds (16 kg)
Gas types
Natural Gas
LP Gas
Venting
Natural Draft
Vent diameter inches 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
1) Depending on gas pressure and altitude.
Table 2

6 720 644 942 (2014/11)520 HN
Appliance details | 9
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 at pressures
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.
BOSCH is constantly improving its products,
therefore specifications are subject to
change without prior notice.

6 720 644 942 (2014/11) 520 HN
10 | Appliance details
3.4 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
39
38
4
5
23
11
40
H
6720608036-01.2Av
8,66" (220)
EFG
4,92"(125)
D
2,50"
(63.5)
1,97"
(50)
3,82"
(97)
A
B
37
10
26
35
34
20
36
C
Dimensions
inches (mm)
520 HN A B C D E F G H
16.73”
(425)
25.75”
(655)
13.15”
(334)
5.11” (130) 21.25”
(540)
2.55” (65) 1.18” (30) 3/4”
Table 3 Dimensions in inches (mm)

6 720 644 942 (2014/11)520 HN
Installation instructions | 11
Fig. 4 Minimum clearances
4 Installation instructions
4.1 Introduction
Please follow these instructions. Failure to follow instructions
may result in:
• Damage or injury.
• Improper operation.
• 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.
4.2 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:
▶1. Common installation practice is to determine the venting
system layout and penetration first, then work back to the
heater.
▶2. Locate the heater where venting, gas and plumbing
connections are feasible and convenient.
▶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.
4.3 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.
Model 520 HN
TOP (A) 12 inches (306 mm)
FRONT (B) 4 inches (100 mm)
BACK 0 inches
SIDES 4 inches (100mm)
BOTTOM (C) 12 inches (306 mm)
Table 4
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
5.6 for draining instructions.
▶ To prevent freeze damage from residual
water in the heater, 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.

6 720 644 942 (2014/11) 520 HN
12 | Installation instructions
Remove cover and inspect.
▶ Remove the flow control and power adjustment knobs.
▶ Unscrew the cover fixing screws, see Fig. 6.
▶ Loosen the two Phillips head screws located on bottom
rear of cover. Remove cover by pulling it outward and then
lifting upwards.
▶ Ensure that the flue terminal is clear.
▶ After inspection, replace front cover and tighten screws.
Install incandescent particle tray.
▶ Install incandescent particle tray using screws provided as
shown in Fig. 5.
Fig. 5 Incandescent particle tray illustration
[1] Screws
[2] Incandescent particle tray
Mounting heater.
The heater must be mounted on a wall using appropriate
anchoring materials. If wall is a stud wall sheathed with
plasterboard, it is recommended that support board(s), either
1x4’s or 1/2" (minimum) plywood first be attached across a
pair of studs and then the heater should be attached to the
support boards, see Fig. 7.
▶ Install the two included L shaped hooks to wall studs or
support board 13 ¼” apart (See Fig. 7).
▶ Hang heater on two L shaped hooks. (See Fig. 8).
Fig. 6 Remove front cover
Fig. 7 Support board
[1] Wall studs
[2] Support board
[3] 1”x4” Space board
WARNING: before starting installation:
▶ check that there are no loose parts
inside the appliance
▶ ensure that gas pipe, gas valve, and
burner have no damage and are
properly fitted.
▶ Read chapter 3.2 to verify proper gas
type and to check all parts are included
in box.
Front cover must be removed in order to
inspect components visually (see
instructions below).
WARNING:
▶ Do not install this appliance on a
carpeted wall.
1
2
3

6 720 644 942 (2014/11)520 HN
Installation instructions | 13
Fig. 8 Secure heater to wall
4.4 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 water 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.
4.5 Venting
▶ Minimum vent pipe diameter: 5inches
▶ Minimum vertical vent height: 6 feet, with no elbows
▶ 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.
DANGER:
▶ Do not reduce the vent pipe size. Do not
put an elbow directly on top of heater.
Failure to follow venting requirements
may cause dangerous exhaust gases to
enter living space.

6 720 644 942 (2014/11) 520 HN
14 | Installation instructions
4.5.1 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.
4.5.2 Vertical venting
▶ 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.
▶ 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.
▶ 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.
▶ 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. 9 and table 5, 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. 9 Flat roof
[1] Listed vent cap
[3] Listed gas vent
[A] Minimum 6 feet (1,8m)
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.
ESTABLISH A ONE
FOOT RISE BEFORE
ANY ELBOWS

6 720 644 942 (2014/11)520 HN
Installation instructions | 15
Fig. 10 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.
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. 12.
Fig. 11 Pitch roof
[1] Listed vent cap
[2] Lowest discharge opening
[3] Listed gas vent
[H] H (minimum) height from roof to lowest discharge
opening
[X] Roof pitch is X/12
[A] Minimum 6 feet (1,8m)
5” X 6” ADAPTOR
USED AT HIGH
ALTITUDE
ESTABLISH A ONE
FOOT RISE
BEFORE
ANY ELBOWS

6 720 644 942 (2014/11) 520 HN
16 | Installation instructions
Fig. 12 Masonry chimney
[1] Listed vent cap
[2] Vent connector
[3] Establish a one foot rise before any elbows
[A] Gas vent
4.6 Gas piping & connections
Before connecting the gas supply, check the rating plate on the
right side of the heater to be sure that the heater is rated for the
same gas to which it will be connected.
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 should conform to CGA B149
INSTALLATION CODES and/or local installation codes.
Mount regulator to gas inlet pipe as shown in Fig. 13. The arrow
on the back of the regulator indicates the direction of gas flow
and should point toward the appliance.
Fig. 13 Installation of Gas Pressure Regulator
Note: The 520 HN comes with a gas pressure regulator. Failure
to install or altering the gas pressure regulator will be a violation
of CSA certification of the unit. The regulator supplied with the
heater is preset for the gas shown on the rating plate to the
correct pressure. It is an appliance level regulator designed for
(low inlet) pressure (less than 1/2 Psig or 14" W.C.).
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 5
WARNING:
▶ DO NOT connect to an unregulated or
high pressure propane line or to a high
pressure commercial natural gas line.
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. If overpressure has occurred, such
as through improper testing of the gas
lines or malfunction of the supply
system, the gas valve must be checked
for safe operation.

6 720 644 942 (2014/11)520 HN
Installation instructions | 17
GAS CONNECTIONS
▶ Install a manual gas shut off valve, on the gas supply line.
▶ Install a union when connecting gas supply.
▶ Attach the appliance regulator to the inlet gas pipe.
▶ The minimum diameter required for any appliance
connector used is ¾” NPT.
▶ National Fuel Gas Code requires that a sediment trap (drip
leg) be installed on gas appliances not so equipped. The
drip leg must be accessible and not subject to freezing
conditions. Install in accordance with the
recommendations of the serving gas supplier.
When connections are made, check for gas leaks at all joints.
Apply some gas leak detection solution to all gas fittings.
Bubbles are a sign of a leak. A combustible gas detector may
also be used to detect for leaks.
HIGH ALTITUDE INSTALLATION
The pressure regulator provided with the heater is adjusted to
deliver the proper gas pressure (as indicated on the rating plate
and in the manual for altitude up to 2000 feet (660 meters)
above sea level. On appliances being installed above 2000 ft
(660 meters) elevation, the inlet gas pressure should be set at
installation to the value shown below.
Note: The gas pressures specified below refer to pressures
taken at the pressure tap on the gas inlet pipe just above the
regulator. See chapter 4.7 for measuring gas pressure.
MAXIMUM INLET GAS FLOW PRESSURE SETTING
DANGER:
▶ If you have a leak, shut off the gas.
Tighten appropriate fittings to stop
leak. Turn the gas on and check again
with a gas leak detection solution.
Never test for gas leaks using a match or
flame.
Altitude Nat. Gas inches Liquid Propane
2 000 ft - 4 500 ft 4.6” 8.4”
Table 6 Above 4.500 ft consult your local gas provider

6 720 644 942 (2014/11) 520 HN
18 | Installation instructions
GAS LINE SIZING
The gas supply piping should be sized according to the applicable code for a maximum draw of 117,000 BTUH. Measure the length
of gas supply line and use the tables in Fig. 14 or the gas line manufacturer’s sizing tables to determine the pipe diameter necessary
to accommodate the BTU demand of the unit. If there are more gas appliances drawing on the same line, size the gas line according
to the total maximum amount of BTU draw for all appliances.
Note: Under sizing the gas line may result in diminished output. See chapter 3.7 for the procedure to measure gas pressure.
FOR NATURAL GAS
Maximum Capacity of pipe in Cubic Feet of Gas per Hour for Gas Pressure of 0.5 Psig or less and a Pressure drop of 0.3 in Water
Column (0.75mbar).(Based on a 0.60 Specific Gravity Gas) Btu numbers given in thousands.
Copper tubing is prohibited for use with Natural Gas in the Commonwealth of Massachusetts and not recommended elsewhere.
Follow boxed numbers for piping just one 520 HN (example: ¾” B.I. Natural Gas pipe for 20 ft (6.1m). will handle 190,000 btu’s
(55.7 kWh). For multiple appliances combine the total btu input load and then refer to applicable chart below.
* EHD = Equivalent Hydraulic Diameter. The greater the value EHD, the greater the gas capacity of the tubing.
Lenght of Black Iron Pipe, Feet
Nominal
Iron
Pipe
Size
Inches
Internal
Diameter
inches 10 20 30 40 50 60 70 80 90 100 125 150 175 200
3/4 0.824 278 190 152 130 115 105 96 90 84 79 72 64 59 55
1 1.049 520 350 285 245 215 195 180 170 160 150 130 120 110 100
1 - 1/4 1.380 1050 730 590 500 440 400 370 350 320 305 275 250 225 210
Table 7
Tube
size,
Inches EHD*
Lenght of Flexible Corrugated Stainless Steel Tubing (CSST), Feet
10 20 30 40 50 60
1/2 18 82 58 47 41 37 34
3/4 23 161 116 96 83 75 68
1 30 330 231 188 162 144 131
1 - 1/4 37 639 456 374 325 292 267
Table 8

6 720 644 942 (2014/11)520 HN
Installation instructions | 19
FOR LP GAS
Maximum Capatity of Pipe in Thousands of BTU per Hour of Undiluted Petroleum Gases (at 11 inches Water Column Inlet Pressure)
(Based on a Pressure Drop of 0.5 Inch Water Column).
* EHD = Equivalent Hydraulic Diameter. The greater the value EHD, the greater the gas capacity of the tubing.
Maximum Capacity of Semi-Rigid copper Tubing in Thousands of BTU per Hour of Undiluted Liquefied Petroleum Gases (at 11
inches Water Column Inlet Pressure).
(Based on a Pressure Drop of 0,5 inch Water Column).
* Source National Fuel Gas Code NFPA 54, ANSI Z223.1
- No Additional Allowance is necessary for an ordinary number of fittings.
Tube size
inches EHD*
Lenght of Flexible Corrugated Stainless Steel Tubing (CSST), Feet
10 20 30 40 50 60
1/2 18 129 91 74 64 58 53
3/4 23 254 183 151 131 118 107
1 30 521 365 297 256 227 207
1 - 1/4 37 971 661 528 449 397 359
Table 9
Nominal
Iron Pipe
Size
inches
Black Iron Pipe
Lenght of pipe, Feet
10 20 30 40 50 60 80 100 125 150 200
1/2 291 200 160 137 122 110 94 84 74 67 58
3/4 608 418 336 287 255 231 197 175 155 140 120
1 1145 787 632 541 480 434 372 330 292 265 227
Table 10
Outside
diameter
Inch
Cooper (LP gas only)
Lenght of Tubing, feet
10 20 30 40 50 60 70 80 90 100
3/8 39 26 21 19 - - ----
1/2 92 62 50 41 37 35 31 29 27 26
5/8 199 131 107 90 79 72 67 62 59 55
3/4 329 216 181 145 131 121 112 104 95 90
Table 11

6 720 644 942 (2014/11) 520 HN
20 | Installation instructions
4.7 Measuring gas pressure
Connecting manometer
▶ Shut off gas.
▶ Remove front cover and locate inlet gas pressure
measuring point on the left side, see Fig. 14.
▶ Loosen screw from test point on the left side and connect
manometer tube on test point.
Fig. 14 Gas pressure measuring point
[A] Inlet tap
Static pressure test
▶ Turn gas supply back on.
▶ Record static gas pressure reading on back page of manual.
Operating pressure test
▶ Turn on all hot water taps served by the water heater.
▶ Turn flow control (right knob) fully clockwise.
▶ Turn power adjustment (left knob) fully counter-clockwise
▶ Turn power adjustment knob fully clockwise.
▶ Operate all other gas appliances on same gas piping system
at maximum output.
▶ Record operating gas pressure reading on back page of
manual.
Gas pressures lower than 5.7" W.C. for Natural Gas or 10.5"
W.C. for LP Gas will result in insufficient degree rise to the hot
water being used, and must be corrected. See Gas Line Sizing
under chapter 4.6.
4.8 Water connections
When facing the heater, the ½ ” cold water inlet is on the bottom
right and the hot water outlet is on the bottom left.
▶ Install unions and shutoff or isolation valves when
connecting plumbing to the water heater. This will facilitate
any necessary cleaning and servicing.
Although water piping throughout the structure may be other
than copper, we require that copper piping or suitably rated
stainless steel flex line piping be used for at least three feet
before and after the heater (follow local codes if more
stringent). Never sweat any rigid piping directly to or beneath
the water connections or damage can occur to the internal
water valve from heating of the pipe. Plastics or other PEX type
plumbing line materials are not allowed for connecting directly
to the water heater. Keep water inlet and outlet pipes to no less
than ½" (12.7mm) diameter to allow the full flow capacity.
It is recommended that all hot water piping be properly
insulated to avoid heat loss.
If the cold and hot connections to the heater are reversed, the
heater will not function. Be certain there are no loose particles
or dirt in the piping. Blow out or flush the lines before
connecting to the water heater. Full port valves must be
installed on both the cold water supply and hot water outlet
lines to facilitate servicing the heater (see Fig. 16). For
installation on a private well system with the use of a pressure
tank, the lowest pressure range setting recommended is 30-50
psi (2.07 and 3.45bar).
Connecting the pressure relief valve (PRV)
A listed pressure relief valve must be installed at the time of
installation. No valve is to be placed between the PRV and the
heater. No reducing coupling or other restriction may be
installed in the discharge line. The discharge line must be a
minimum of 4” above a drain and installed such that it allows
complete drainage of both the PRV and the line.
The location of the PRV must be readily accessible for servicing
or replacement, and be mounted as close to the water heater as
possible. See Fig. 15. To install the PRV, a suitable fitting
connected to an extension on a “T” fitting can be sweated to the
hot water line.
Support all piping.
6720608032-13.1Av
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