INSTALLATION AND OPERATING INSTRUCTIONS FOR AUTOMATIC
INSTANTANEOUS TYPE WATER HEATERS FOR USE WITH NATURAL AND
LIQUEFIED PETROLEUM GAS
MODEL 125B LPS and 125B NGS (Thermostatically Modulated)
Suitable for heating potable water only
Not approved for space heating purposes
Intended for domestic hot water with preheated inlet water as with solar hot water.
WARNING
If the information in this manual is not followed exactly, a
fire or explosion may result causing property damage,
personal injury or death.
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.
WARNING: 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. Upon
completion of the installation, these instructions should
be handed to the user of the appliance for future
reference.
6 720 606 518 US (04.11) AL
In the Commonwealth of Massachusetts this product
must be installed by a licensed plumber or gas fitter.
FEATURING: Automatic Variable Power Modulating Gas
Valve with Thermostatic Control
Warning: If you do not follow these instructions exactly, a
fire or explosion may result causing property damage,
personal injury or loss of life.
WHAT TO DO IF YOU SMELL GAS
- 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.
This well engineered, gas water heater has been specially
designed to operate with incoming pre-heated water:
It operates on the principle of heating water instantaneously
“on demand”. When a hot water faucet is opened, cold water
flows through the coils of the heat exchanger in the Aquastar.
This same flow opens the gas valve, and the burners are
ignited by the pilot flame. The heat exchanger coils absorb
the heat generated by the burners and transfer heat to the
water. When the hot water faucet is shut off, the gas valve
automatically closes and the burners turn off. Your hot water
faucet is an ignition key to turn on the water heater, giving
you control over your hot water energy use. Each time you
turn off your hot water faucet, you also shut off the water
heater. On the Aquastar “S” model, if the incoming water is
colder than the thermostat setting of the heater, the burners
will ignite to heat the water in order to boost it and maintain
it at the temperature setting. If the incoming water has been
pre-heated, (ie) solar, and this water temperature is warm
then the the burners will modulate down accordingly, or
shut down completely if the temperature is as hot or hotter
than the heater thermostat setting. The Aquastar 125 BS is
the perfect backup to a solar hot water system.
AquaStar 125B LPS and 125B NGS Specifications
Gas Input max.: 117,000 Btu/hr
min.: 23,400 Btu/hr
Water Connection 1/2” Thread fitting NPT
H x W x D 29 3/4” x 18 1/4” x 8 3/4"
Vent 5”
Gas Connection 1/2” NPT thread
Min. Water Pressure 18 Psi at 4 GPM
Max. Water Pressure 150 Psi
Shipping Weight 44 LB
Net Weight 42 LB
1.8 GPM at 90° rise
FEATURES
- High Quality Materials for Long Working Life.
- Copper heating coils for endless supply of hot water.
- Burner output proportional to hot water flow demand for
maximum energy efficiency.
- Automatic Thermostatic Control for steady hot water
temperature
- Input BTU’s modulate to zero to prevent overheating of
water from pre-heat source
- Stainless steel burners with stabilized blue flame.
- Built-in corrosion resistant draft inducer.
- Compact space saver: mounts on a wall with two hooks.
- Easily removable one-piece cover.
3.7 GPM at 45° rise
Min. Water Flow 1/2 gal/min
LP GAS Supply Pressure
(before Aquastar regulator)min.: 11” W.C.
max.: 14” W.C.*
Required LP GAS Pressure at inlet
tap while Aquastar is operating: 10.5” W.C.
LP GAS Burner Manifold pressure while Aquastar
is operating at maximum input:9.0” W.C.
Natural Gas Supply Pressure
(before Aquastar regulator)min.: 7” W.C.
max.: 14” W.C.*
Required Natural Gas Pressure at inlet tap
while Aquastar is operating:5.7” W.C.
Natural Gas Burner Manifold pressure while Aquastar is
operating at maximum input:4.2” W.C.
* Inlet gas pressure before Aquastar regulator must not
exceed this value. Pressure may need to be adjusted for
high altitudes, see page 11.
- Easy one person installation.
- Adjustable water flow restrictor to ensure that water flow
demand will not exceed the heating capacity of the heater.
UNPACKING THE AQUASTAR HEATER
- Easy pilot flame lighting with push button piezo ignition.
This heater is packed securely. The box includes two water
connection fittings, a gas pressure regulator, a pressure relief
BOSCH is constantly improving our products, therefore
specifications are subject to change without prior notice.
26 720 606 518
valve, an incandescent particle tray, two hooks for hanging
the heater, this manual, a warranty statement and a warranty
registration card. Do not lose this manual, as there is acharge for replacement. Please complete and return the
enclosed warranty registration card.
D861_059
FRONT VIEWSIDE VIEW
MINIMUM INSTALLATION CLEARANCES FROM COMBUSTIBLE AND NON
COMBUSTIBLE MATERIALS FOR ALCOVE OR CLOSET INSTALLATIONS
MODEL 125BS
TOP (A)12 "
FRONT (B)4 "
BACK0 "
SIDES4 "
FLOOR (C) 12 "
VENT DIAMETER5 "
AQUASTAR MODEL 125BS
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GENERAL RULES TO FOLLOW
FOR SAFE OPERATION
PROPER LOCATION FOR INSTALLING YOUR
HEATER
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. Correct
combustion air supply and flue pipe installation are very
important. If not installed correctly, fatal accidents can be
caused by lack of air, carbon monoxide poisoning or fire.
3. The place where you install the heater must have enough
ventilation. The National Fire Codes do not allow gas fired
water heater installation in bathrooms, bedrooms or any
occupied rooms normally kept closed. See the section below
on locating the heater.
4. You must vent your heater. See section on VENTING,
Page 6.
5. The appliance must be disconnected from the gas supply
piping system during any pressure testing at pressures in
excess of 1/2 Psig (3.5 kPa).
The appliance must be isolated from the gas supply piping
system by closing its individual manual shutoff valve during
any pressure testing of the gas supply piping system at test
pressures equal to or more than 1/2 Psig (3.5Kpa). The
appliance and its gas connection must be leak tested before
placing the appliance in operation.
6. Keep water heater area clear and free from combustibles
and flammable liquids. Do not locate the heater over any
material which might burn.
7. Correct gas pressure is critical for the optimum
operation of this heater (see specifications on page 2). 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 the section on connecting the gas supply.
8. 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.
9. 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.
Carefully select the location of your new heater. For your
safety and for proper heater operation, you must provide an
abundant supply of combustion air and a proper venting
installation.
The heater may still operate even when improperly vented.
It will, however, be less efficient and could eventually damage
the heater. It could even result in human sickness or death
due to oxygen deprivation and carbon monoxide poisoning.
Follow the guidelines below:
1. Place your heater as close to a vent or chimney as
possible.
2. National building codes require that you do not install
this appliance in bathrooms, bedrooms, unvented closet or
any occupied rooms normally kept closed.
3. Simultaneous operation of other appliances such as
exhaust fans, ventilation systems, clothes dryers, fireplaces
or wood stoves could create a vacuum effect in your home
which could cause dangerous combustion by-products to
spill back into your home rather than venting to the outside
through the flue. Confirm that your Aquastar is venting
properly when all these other appliances are running. See
section on venting.
Do not obstruct the flow of combustion and ventilation
air to the appliance. If installed near a clothes dryer it is
very important that the dryer be properly vented. Failure to
properly vent a dryer could result in a gradual accumulation
of lint on the water heater fin coils and burners, leading to a
dangerous condition of vent blockage and poor unsafe
combustion.
4. Your hot water lines should be kept short to save energy.
It is always best to have hot water lines insulated.
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.
This heater is neither designed for not approved for
outside installation. Drain the heater entirely if freezing
temperatures are anticipated in the area where heater is
installed by disconnecting both the inlet and outletelbow
connections at the rear of heater. Additionally remove the
drain plug under the water valve. See Fig 0.
This product is not approved for manufactured homes
(mobile home), recreational vehicles (RV) or boats.
Reference ANSI Z21.10.3.
This product is neither designed or approved for outside
installations.
Fig. 0 - Water heater drain plug
46 720 606 518
WARNING: Flammable materials, gasoline,
pressurized containers, or any other items or articles
that are potentially 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.
COMBUSTION AIR REQUIREMENTS
The AquaStar water heater holds cold water in its copper
heat exchanger and brass water valve when not in use.
Because of this, any cold air that comes in 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 area are not being supplied with a sufficient amount
of make-up air. A wood stove or furnace can rob the makeup air in the AquaStar’s vent pipe, leaving the cold infiltrating
air capable of freezing the cold water in the AquaStar heat
exchanger. More make up air is the solution. Follow the
instructions on venting and checking adequacy of make up
air. A HVAC specialist should be used 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 AquaStar 125B “S” alone.
b) In unconfined spaces in buildings of conventional frame,
masonry, or metal construction, infiltration is normally
adequate to provide air for combustion, ventilation, and
dilution of flue gasses.
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.
Air Vents
(10 ¾ X 10 ¾ in. each)
125BS
125BS
Air Vents
(5 ½ X 5 ½ in. each)
Louvers, grills and screens have a blocking effect. If the
effective free area is not known, increase the sizes of your
openings by 75% if your louvers are wood and by 30% 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.
CLEARANCES
The Aquastar 125 B “S” is design certified for installation
on a combustible wall and for installation in an alcove or
closet with the minimum clearances to combustible and non
-combustible construction listed below
A. Top 12 inches (306 mm)
B. Front 4 inches (102 mm)
C. Back 0 inches
D. Sides 4 inches (102mm)
E. Bottom 12 inches (306 mm)
Clearance from vent is dependent upon the clearance rating
of the venting material used. For example, type B-a vent is
approved for 1 inch clearance.
Note: Typically, the minimum clearance to combustible
materials should not be less than 6” for single wall flue
pipe. Note that this clearance can be reduced if combustible
materials are protected as per table VI of the National Fuel
Gas Code or if Type B gas vent is used.
56 720 606 518
MOU NT I NG IN STA LLATI ON
The Aquastar 125 B “S” is design certified for mounting on
a wall.
Secure the two L shaped hooks provided with the heater to
a wall surface. Place them 13 ¼ inches apart as shown in
Fig 1. Do not install this appliance on a carpeted wall or
over floor covering which is combustible, such as carpet.
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 1.
Expansion and contraction of piping due to changing water
temperature in the pipes imparts movement to the heater
which, if mounted directly to a brittle, friable board, such as
plasterboard, can cause failure of mounting.
In earthquake-prone zones, CEC recommends that installers
use a large washer and lag screw through the existing holes
used to hang the heater to affix the upper third of the heater
to the mounting board. To affix the lower third of the heater,
CEC recommends that two new holes be drilled in the
heater’s frame, each one 16 inches below the top two holes,
and that washers and lag screws be used to secure the
lower portion of the heater to a spacing board.
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. Also, each burner orifice is stamped with a number
(79 for LPG and 120 for Natural Gas).
The incandescent particle tray (shipped loose in the carton
with the water heater) must be attached at the bottom of
the water heater front cover at the time of installation. Use
the screws provided. See figure 2
SCREWS
INCANDESCENT PARTICLE TRAY
Fig. 2 - Incandescent Particle Tray Illustration
13 ¼ ”
SUPPORT BOARD
Fig. 1 - Mounting the Heater
WALL STUDS
1” X 4”
SPACE BOARD
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VENTING
Vent pipe connection. WARNING: Do not reduce the vent pipe size. See Fig. 3 for high altitude installations
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.
The heater should never be common vented with a mechanically vented appliance. Single wall vent pipe is not
recommended, if used consult the National Fuel Gas Code.
Horizontally venting to a sidewall vent terminator or a vertically constructed vent stack along an outside wall of a building
is not permissible. A Powervent (Model AQ-1), with a proof-of-draft safety interlock device, is required and is available in
order to sidewall vent. Contact your dealer. In the Commonwealth of Massachusetts: Powervented applications must
utilize proof-of-draft safety interlock device.
VERTICAL GAS VENT: A 5 inch diameter gas vent constructed of double wall Type B gas vent is recommended. 6 inch is
required in elevations greater than 2000 feet, see Fig. 3. 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 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.
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 Figure A or B and their table, 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’s passed 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).
LISTED VENT CAP
LOWEST DISCHARGE OPENING
H (minimum) height
from roof to lowest
discharge opening
LISTED GAS VENT
Figure AFigure B
LISTED VENT CAP
X
12
ROOF PITCH
IS X/12
GAS VENT TERMINATIONS FOR LISTED VENT CAPS
Roof pitchH (minimum) feetmeters
Flat to 6/12
6/12 to 7/121.250.38
Over 7/12 to 8/121.50.46
Over 8/12 to 9/122.00.61
Over 9/12 to 10/12
Over 10/12 to 11/12
Over 11/12 to 12/124.01.22
Over 12/12 to 14/125.01.52
Over 14/12 to 16/126.01.83
Over 16/12 to 18/12
Over 18/12 to 20/12
Over 20/12 to 21/12
1.00.30
2.50.76
3.250.99
7.02.13
7.52.27
8.02.44
76 720 606 518
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