Bosch GWH-635-ES User Manual

Index

Index

1 Warning 2

2 Appliance details 4

2.1 Features 4

2.2 GWH-635-ES Specifications (Technical data) 4

2.3 Dimensions and Minimum installation clearances 6

2.4 General rules to follow for safe operation 7

2.5 Proper location for installing your heater 7

2.6 Clearances 8

2.7 Mounting installation 8

2.8 Combustion air requirements 8

2.9 Venting 9

2.9.1 Venting options 12

2.10 Gas piping & connections 15

2.11 Gas line sizing 17

2.12 Measuring gas pressure 17

2.12.1 Connecting Manometer 17

2.12.2 Static Pressure Test 17

2.12.3 Operating Pressure Test 17

2.13 Water connections 18

2.14 Electrical connections 19

2.15 Operating instructions 19

2.16 For your safety read before operating your water heater 19

2.17 Lighting and operating instructions 19

3 Operation instructions 21

3.1 Power 21

3.2 Temperature selection 21

3.3 Use of remote control accessory 23

3.4 Operation 23

3.5 Reset button 23

3.6 Program button 23

3.7 Locked condition 23

4 Maintenance and service 24

5 Troubleshooting 24

1 Warning

Warning: If the information in this

manual is not followed exactly, a fire or
explosion may result causing property
damage, personal injury or death.

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.

Featuring

Electronic Ignition and Power Venting

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: 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 from lack of air, carbon monoxide
poisoning or fire.

6 Electrical diagram 27

7 GWH-635-ES Functional scheme 28

8 Interior components diagram and parts list 29

8.1 Interior components 29

8.2 Components diagram 30

8.3 Parts list 31

9 Special adjustment for measuring and adjusting CO2
levels 32

10 Protecting the environment 34

11 Fifteen Year Limited Warranty 35

2

Warning: Exhaust gas must be vented
to outside using proper vent material
suitable for category III vent systems
and temperatures up to 480°F. Vent
and combustion air connector piping
must be sealed gas-tight to prevent
possibility of flue gas spillage, carbon
monoxide emissions and risk of fire,
resulting in severe personal injury or
death.

Warning: Place the heater in a location
where water leaks will do NO DAMAGE
to adjacent areas or lower floors.

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Warning: 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.

Warning: Shock hazard line voltage is
present. Before servicing the water
heater, turn off the electrical power to
the water heater at the main disconnect
or circuit breaker. Failure to do so could
result in severe personal injury or death.

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.

Warning

Fig. 1

Warning: 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 psig.

FCC:
This device complies with Part 15 of the FCC rules.
Operation is subject to the following two conditions: (1)
This device may not cause harmful interference, and (2)
this device must accept any interference received,
including interference that may cause undesired
operation.

Caution: Any changes or
modifications not expressly approved
by the party responsible for compliance
could void the user’s authority to
operate the equipment.

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Fig. 2

3

Appliance details

i

2 Appliance details

2.1 Features

Parts

• Touch Pad interface control

• High power pre-mix compact burner with low Nox
emissions

• Modulating Gas Valve with constant gas:air ratio
control

• Modulating water valve for improved comfort and
temperature control.

Safety

• Flame sensor (ionization) rod

• Overheat sensor

• Temperature limiter

• Fan speed monitoring.

High Quality Materials for Long Working Life

• Copper heat exchanger

• High efficiency Ceramat Burner

• Compact space saver: mounts on a wall with a
supplied bracket.

• Easily removable one-piece cover.

Features

• LCD Display

• On/Off and Temperature control switches

• Reset button

• Program Key (Selectable temperature default)

• Failure codes for easy diagnostic and repair.

Accessories

• Optional wireless remote control accessory to
operate with the appliance

• Vent termination kit.

BOSCH is constantly improving its
products, therefore specifications are
subject to change without prior notice.

2.2 GWH-635-ES Specifications
(Technical data)

Approved in US/Canada

Capacity

Maximum flow rate: 6.35 GPM (24 l/min) at a 45°F
(25°C) rise.

Maximum output

142,968 Btu/h (41.8 kW)

Maximum input

175,000 Btu/h (51.2 kW)

Efficiency in %

Recovery efficiency 86.5%

Min. Output

31,131 Btu/h (9.1 kW)

Temperature Control

Selection range: 100°F (38°C) - 140°F (60°C)
Default temperature: 122°F (50°C)
Stability: +/- 2°F (+/- 1°C)

Gas Requirement

Gas connection (inches) - ¾”

Inlet gas pressure under operation (with a high hot
water flow rate)*

• Propane: 11” - 14” water column

• Natural Gas: 5” - 14” water column.

* To measure Gas Pressure, see Measuring Gas
Pressure, chapter 2.12.

Venting

A condensate trap is integrated into the exhaust flue
gas collar of the heater, the supplied condensate drain
tube must be installed to it for proper removal of
condensate from the trap. See chapter 2.9 for Venting.

Water

• Hot water connection (inches) - ¾”

• Cold water connection (inches) - ¾”

• Water valve material: Polymer (PPS) (Polypropylene

Sulfid)

• Minimum water flow: 0.8 gallon/minute (3 l/m)

• Minimum recommended water pressure: 30 PSI

(2.07 bar)

• Connections:

– Bottom of heater

4

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Appliance details

Combustion

• NOx ≤ 55 ppm

• CO ≤ 250 ppm

• CO2 level set from factory, see chapter 9.

Dimensions

• Depth (in): 8 ½” (220 mm)

• Width (in): 15 ¾” (400 mm)

• Height (in): 23 ½” (600 mm)

• Weight: 47 pounds (21 kg).

Gas types

Natural Gas.
LP Gas.
Converting the gas type can only be done by a certified
gas technician with a calibrated CO2 analyzer.
Call BBTNA for conversion instructions.

Voltage

120 V AC (50/60 Hz)

Amperage

IDLE - 40 mA
Operation - ≤ 2,5 A

Do not lose this manual. Please complete and return
the enclosed product registration card.

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.

To remove front cover

• Loosen the two Philips head screws located on front
panel (beneath plastic decal shields if they are
already attached, see Fig. 3)

• Lift front cover panel upward and remove.

Noise

≤ 50 db (A)

Safety devices

• Flame failure device (ionization flame rod sensor)

• Pressure relief valve (supplied with heater)

• Over heat prevention (temperature limiter).

Water resistant

IP X4 (protection against water drops)

UNPACKING THE GWH-635-ES HEATER

This heater is packed securely.

The box includes:

• Pressure relief valve (150 psi / 200,000 Btu rating)

• Bracket for wall hanging the heater

• Exhaust vent adaptor (with 4 screws and gasket
provided)

• Condensate drain tube kit

• Combustion air inlet adaptor (with 3 screws and gas­ket provided)

• Plastic decal shields for covering front cover screws
and control panel, installer should affix these decals
to the front of the unit after installation is complete.
See Fig. 3

• Installation manual

• Product registration card

Fig. 3 Remove front cover

The GWH-635-ES is not approved or designed
for:

• Manufactured (mobile) homes, RV's or boats

• Heating or other recirculating/pumping applications*

• Outdoor installation (use only Outdoor Model GWH­635-ESO)

• Solar/preheat backup or high temperature booster
use.

* This includes domestic hot water circulator pump loop
systems that may previously exist in a home hot water
system. The use of a small electric mini-tank (4-6 gallon
size) should be used for this application; when
designed so the pump will circulate the hot water in the
mini-tank only and through the building's hot water
return loop (timed or thermostatic controlled operation
of the pump is commonly done). The GWH-635-ES
should be plumbed in line before the mini-tank water
heater, contact BBTNA if further instruction is needed.

• Energy Guide label.

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Appliance details

2.3 Dimensions and Minimum installation clearances

Fig. 4 Dimensions

1 Cover
2 On/Off switch
3 Reset button
4 LCD display
5 Program button
6 Temperature buttons

Fig. 5 Minimum clearances

Model GWH-635-ES

TOP (A) 12”

FRONT (B) 1”

BACK 0”

SIDES 1”

FLOOR (C) 12”

VENT DIAMETER 3”

Table 1 Minimum clearances

6

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Appliance details

2.4 General rules to follow for safe
operation

B 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.

B 2. Carefully plan where you install the heater. Correct

combustion air supply and vent pipe installation are
very important. If not installed correctly, fatal
accidents can be caused by lack of air, carbon
monoxide poisoning or fire.

B 3. When the unit is installed indoors and ROOM

SEALED (twin pipe) it is permitted to be located in
bathrooms, bedrooms and occupied rooms that are
normally kept closed. See chapter 2.9. If the unit will
be installed indoors and use indoor combustion air,
the place where you install the heater must have
enough ventilation. The National Fire Codes do

not allow UNSEALED gas fired water heater
installations in bathrooms, bedrooms or any
occupied rooms normally kept closed. See

chapter 2.5 and 2.8.

B 4. You must vent your heater. See section on

VENTING.

B 5. The appliance and its gas connection must be leak

tested before placing the appliance in operation.
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).

B 6. Keep water heater area clear and free from

combustibles and flammable liquids. Do not locate
the heater over any material which might burn.

B 7. 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 the section on connecting the gas supply.

B 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. Note: manual gas
shutoff valve is not supplied with the heater.

B 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

2.5 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. Locate the heater where venting, gas and

plumbing connections are feasible and convenient.

B 2. It is strongly recommended that the heater be

installed as a ROOM SEALED heater (twin pipe). If
the heater will be installed as an UNSEALED heater
(sing368 0 Td(r)Tj3.12233 0 Td(e)Tj5.28395 0

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Appliance details

2.6 Clearances

The GWH-635-ES is design certified for installation on
a combustible wall (see 2.7 Mounting installation)
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 below. See also Fig. 5.

A. Top 12 inches (306 mm)
B. Front 1 inches (25 mm)
C. Back 0 inches
D. Sides 1 inches (25 mm)
E. Bottom 12 inches (306 mm)

Clearances from any exhaust vent pipe are dependent
upon the clearance requirements of the stainless steel
vent pipe manufacturer. Single wall stainless steel
(AL29-4C) vent pipe (vent type rated for Category III
appliances) must be used when exhaust venting this
appliance. See 2.9 Venting.

2.7 Mounting installation

The GWH-635-ES is design certified for mounting on a
wall. Secure the wall mounting bracket provided with
the heater to a wall surface. See Fig. 6.
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 the mounting bracket is unable to line up on two wall
studs it is recommended that support board(s), either
1x4's or ½" (minimum) plywood first be attached across
a pair of studs and then the heater should be attached
to the support boards. The heater should be kept level
on the wall surface. See Fig. 6.
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.

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.

Fig. 6 Mounting the heater

2.8 Combustion air requirements

The GWH-635-E5S is a sealeg water

heat er and it

8

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Appliance details

construction, infiltration air is normally adequate to
provide air for combustion.

• Appliances located in confined spaces:
The confined space must be provided with two
permanent openings, one commencing within 12
inches (304.8mm) of the top and one commencing
within 12 inches (304.8mm) of the bottom of the
enclosure. Each opening must have a minimum free
area of one square inch per:

– 1000 Btu/hr (292.81 Watts) if all air is taken from

inside the building

– 2000 Btu/hr (585.62 Watts) if all air is taken from

the outside by horizontal ducts

– 4000 Btu/hr (1171.24 Watts)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
(304.8mm) of the ceiling of the enclosure. This opening
must have a minimum free area of one square inch per:

– 3000 Btu/hr (878.43 Watts) if all air is taken from

the outside by a direct opening or vertical duct.

Louvers, grills and screens have a blocking effect, when
used, increase the sizes of your openings by 300% for
wood louvers (as wood type will reduce the free air by
75%) and 40% for metal louvers (as metal will reduce
the free air by 30%). Refer to the National Fuel Gas
Code for complete information. In buildings of tight
construction all air should be taken from outside.

NOTE: It is not recommended to use interior
room air (SINGLE PIPE vent system) in areas that
commonly experience below freezing
temperatures. Clothes dryers, furnaces,
woodstoves, bathroom or kitchen fans or other
gas appliances can create negative air pressure
when operating by removing air from the
building. Cold air will be drawn back into the
building, and if drawn through the water heater a
freezing situation may occur. TWIN PIPE (room
sealed) method of venting is recommended, see
page 12.
NOTE: When installed in beauty shops, barber
shops, or other facilities where chemicals that
generate corrosive or flammable products such
as aerosol sprays are routinely used, shall be
installed as sealed unit following the TWIN PIPE
SYSTEM method of venting.

2.9 Venting

Warning: Do not reduce the vent

(exhaust and combustion) pipe sizes
and do not common vent with any other
vented appliance or stove.

NOTE: This appliance's exhaust must be vented
to the outside1 with sealed stainless steel vent
pipe (AL29-4C), the minimum vent length is 3 feet
(a 90 degree vent elbow is equivalent to 2 ½ feet).
The appliance's flue gasses are under positive
pressure and must travel through a stainless
steel 3" or 4" pipe that is sealed gas tight.
NOTE: The exhaust collar on the water heater is
3" diameter and its collar must always be used, a
3" to 4" increaser will be required to be first
connected to the exhaust collar when 4" venting
is used. Different stainless steel vent
manufacturer's have different joint systems, do
not mix vent pipe or joining methods from
different manufacturer's.
Stainless steel vent pipe is equipped with sealing
gaskets for ease of installation, proper safety
and durability. The heater shall not be vented in
combination with any other appliance; the
appliance must only be vented with a dedicated
sealed vent system.

Z flex Protech Heat Fab BBTNA

3” VENTING

3” Horizontal

Terminal 2SVSTB03 FSTB3 9390 TEE 2SVSTB03

3” Vertical

terminal

4” VENTING

Requires a 3”

to 4” Increaser 2SVI0304 FS0304TI 9374 2SVI0304

4” Horizontal

terminal

4” Vertical

terminal

Table 2 Terminals/Adapters Part Numbers

2SVSRCF03 FSRC3 5300CI 2SVSRCF03

2SVSRTF04 FSTB4 9490TEE FXHOOD

2SVSRCF04 FSRC4 5400CI ----------

Caution: The vent system must be
installed by a qualified agency in
accordance with these instructions. If
improperly installed a hazardous
condition such as explosion or Carbon
Monoxide poisoning could result.
BBTNA will not be responsible for
improperly installed appliances.

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Establish vent clearances that comply with the vent
manufacturer's specifications. In all cases follow local
codes. See table 3.

9

Appliance details

The maximum flue gas exhaust temperature on the GWH-635-ES is 437°F (225°C)

Venting
Options

Room
sealed
(twin pipe)

Open
combustion
(single
pipe)

Exhaust vent is always fan assisted. Installation of exhaust vent and combustion air piping may be run vertically or horizontally
and in separate directions if required.

+

The exhaust collar on the water heater is 3" diameter and its collar must always be used, a 3" to 4" increaser will be required

to be first connected to the exhaust collar when 4" venting is used.
* A maximum of three 90 degree elbows are permitted in both the exhaust and combustion air vent lengths. The total vent
length must be reduced by 1 ¼ feet for every 45° elbow used in the vent system.
** Stainless steel (AL29-4C) vent pipe is manufacturerd by Z-Flex, Protech and Heat Fab. NOTE: clearance distances are
variable depending if the vent pipe is installed in an enclosed or unenclosed space, the exhaust flue gas temperature and the
orientation of the vent pipe.

Exhaust
vent
diameter
and
material

3 or 4+
inch
stainless
steel
(AL29-4C)
sealed vent
pipe

3 or 4+
inch
stainless
steel
(AL29-4C)
sealed vent
pipe

* Exhaust
vent
maximum
length

26 feet (8
m) with one
elbow. Less
2½ feet for
each
additional
90° elbow

26 feet (8
m) with one
elbow. Less
2½ feet for
each
additional
90° elbow

* Exhaust
vent
minimum
length

3 feet 3 inch PVC,

3 feet See

Combustion
air pipe
diameter
and material

aluminum or
galvanized
pipe

chapter 2.8

Combustion
air pipe
maximum
length

26 feet (8
m) with one
elbow. Less
2½ feet for
each
additional
90° elbow

See
chapter 2.8

Vent pipe
clearances
within an
unenclosed
space

** See vent
manufacturer's
specifications

** See vent
manufacturer's
specifications

Vent pipe
clearances
within an
enclosed
space

** See vent
manufacturer's
specifications

** See vent
manufacturer's
specifications

Table 3

Minimum exhaust vent size and length

The appliance should be located as close to the point
of termination as possible. The maximum vent length is
26 feet (8 m) with one 90 degree elbow. Subtract 2½
feet from the total vent length for each additional 90°
elbow used (a maximum of three 90° elbows are
permitted in the total vent length), or subtract 1 ¼ feet
for every 45° elbow used. Horizontal sections of vent
must pitch ¼" for every foot of horizontal length, to
prevent the pooling of condensate, and be supported at
4 foot intervals with overhead hangers.
Note: Listed thimbles or collars are necessary to pass
through wall and ceiling partitions. If the vent system
passes through combustible areas where the vent
clearance requirements cannot be maintained, it is
permissible to chase straight sections of sealed 3 inch
single wall vent through 4 inch (or greater) Type-B vent.
The distance to combustibles using this chase
technique is 1 inch. Note: Type-B vent should never

be used as the actual exhaust vent system for the
appliance, as it is not gas tight.

Fig. 7

Maximum exhaust vent and combustion air inlet
lengths

10

Fig. 8

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Appliance details

Note: reduce 2½ ft for each 90° elbow used after the
first one, reduce 1 ¼ ft for each 45° elbow.

Vent Safety System

The GWH-635-ES will shut down if inadequate exhaust
venting is detected or a lack of combustion air is
provided to the unit; see troubleshooting section on
page 24. See error code to confirm error, correct the
problem and then reset the heater before operating.

Attaching the exhaust and air inlet connection
adaptors to the top of the heater

Use of the external condensate drain tube kit
(supplied with the heater) on the exhaust collar

B The condensate drain tube kit must be used for all

installation types. Failure to install condensate
drain will void the warranty.

B When installing the condensate drain tube kit at the

exhaust collar (see diagram below), be sure to form a
trap by means of a 3" (76.2 mm) loop filled with
water. The supplied tube is 3/8" ID high temperature
silicone and must be attached to the condensate
tapping on the exhaust collar with its supplied gear
clamp (first remove screw at tapping point).

B To increase tube length, connect vinyl type tubing

after the supplied tube.

B The condensate must be disposed of according to

local regulations.

Fig. 9

Fig. 10

B Attach the flue gas exhaust accessory (8 705 504

114) to the top of the unit (position 1) using the 4
screws and gasket provided, and fully insert 3"
stainless steel vent pipe into the accessory and
tighten the clamp (position 2).

B Attach the combustion air inlet accessory (8 705

504 115) to the top of the unit (position 3) using the
3 screws and gasket provided, and fully insert 3"
combustion air pipe into the accessory and tighten
the clamp (position 4). NOTE: The appliance has the
possibility to mount the combustion air inlet
accessory on the top right or on the top left side of
the heater. The combustion air inlet that is not used
must be kept sealed.

Fig. 11

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Appliance details

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i

2.9.1 Venting options

Installing this water heater as a room sealed (TWIN
PIPE SYSTEM) is the recommended method. Contact
BBTNA or dealer for available vent termination kits and
vent materials for this water heater.

Exhaust venting shall be done with 3" or
4" stainless steel (AL29-4C) vent pipe.

Room sealed installation (TWIN PIPE SYSTEM)

Fig. 12

Combustion air pipe: ≤ 26 ft (8 m)
Exhaust vent pipe: ≤ 26 ft (8 m)

Open combustion installation (SINGLE PIPE
SYSTEM)

Not recommended in cold climate areas, see
Chapter 2.8.

Fig. 14

Exhaust vent pipe: ≤ 26 ft (8 m)

Fig. 13

Combustion air pipe: ≤ 26 ft (8 m)

Exhaust vent pipe: A+B+C ≤ 23½ ft (7.2 m)
Note: reduce 2½ ft for each 90° elbow used after the
first one, reduce 1 ¼ ft for each 45° elbow.
A maximum of three 90-degree elbows are permitted in
both the exhaust and combustion air vent lengths.

The exhaust vent pipe and combustion air
pipe can be run vertically or horizontally.
Maximum length for each individual pipe is
26 feet (8 m) with one elbow, for each
additional 90° elbow after the first elbow
you must reduce 2½ feet from the total
vent length, or 1 ¼ feet for each 45°
elbow.

12

Fig. 15

Exhaust vent pipe: A+B+C ≤ 23½ ft (7.2 m)

The exhaust vent system must vent directly to the
outside of the building and an adequate amount of
indoor combustion air must be provided for this
installation. See chapter 2.8.
Connecting a one piece 90 degree elbow pipe to the
combustion air inlet adaptor is necessary, this will
prevent debris or objects from ever falling into the inlet
opening.
Note: reduce 2½ ft for each elbow used after the first
one, reduce 1 ¼ ft for each 45° elbow.
A maximum of three 90-degree elbows are permitted.

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Recommended exhaust vent terminator position

Fig. 16

Appliance details

Ref. Description Minimum distance

A

B

C From any internal corner 12 in

D*

E

F From a terminator facing a terminator 48 in

G Vertically between two exhaust vent terminators on the same wall 60 in

H Horizontally between two exhaust vent terminators on the same wall 12 in

I**

J From any external corner 12 in

K

Directly below an opening; operable windows, doors and any non­mechanical fresh air openings

Below a gutter, sanitary pipework or eaves 24 in

Below a gutter, sanitary pipework or eaves, protected by metal
shielding

Above ground 12 in

Above a paved sidewalk 7 ft

From an opposing wall or structure facing the termination 24 in

From any other building opening, gas utility meter, service regulator
or the like

Horizontally from combustion air inlet of GWH-635-ES

Vertically above or below combustion air inlet of GWH-635-ES

From the combustion air inlet of any other equipment 6 ft

Horizontally from an opening; operable windows, doors and any
non-mechanical fresh air openings

36 in

12 in

36 in

36 in

12 in

L

Vertically from a wall, roof slope, or obstruction (venting through a
flat or pitched roof)

see ABOVE THE ROOF

requirements on following page

Table 4

* Subject to local codes and anticipated snow level
** Other equipment that operates with a mechanical air inlet may require greater distances, reference manufacturer's instructions

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Supporting the exhaust vent system

The venting materials and accessories
required to properly install the water
heater are available from BBTNA and their
distributors.

Fig. 17 Horizontal side wall venting installation

(combustion air piping not being shown)

Fig. 18 Above the roof clearance requirements from

rain cap (combustion air piping not being
shown)

B A condensate drain tube must be attached to the

exhaust collar of the heater for all vent type
applications, see page 11.

Fig. 19 Vertical venting installation (combustion air

piping not being shown)

A condensate drain tube must be attached to the
exhaust collar of the heater for all vent type applications,
see page 11.

14

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Gas piping

Inlet gas particle screen

2.10

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 with CGA
B149 INSTALLATION CODES and/or local installation
codes.

GAS LINE SIZING

The gas supply piping should be sized according to the
National Fuel Gas Code for a maximum draw of
175,000 BTUH. First determine the effective length of
the gas supply line by measuring the actual length of
piping, and then adding 5 ft. (1.52m) for every elbow or
“T” to the actual length. Use the charts in Fig. 22 to
determine the pipe diameter necessary to
accommodate the BTU (Wh) demand of the unit. If
there are more gas drawing appliances on the line, size
according to the maximum amount of BTU (Wh)
demand.

Note: It is important that if any flexible gas line is used,
above or below ground between the gas supply meter/
regulator and the water heater, that it be sized properly.
Consult the gas sizing specification tables provided by
the flexible gas line manufacturer and sample CSST
flexible gas line tables in Figure 22.

Gas piping & connections

Fig. 20 Vertical venting installation - Masonry

Chimney (combustion air piping not being
shown)

A condensate drain tube must be attached to the
exhaust collar of the heater for all vent type applications,
see page, see page 11.

6 720 607 072

Fig. 21

B Install a manual gas shut off valve, on the gas supply

line.

B The use of a union when connecting gas pipe to the

gas inlet connection is critical, this will facilitate any
necessary servicing and cleaning of the inlet gas
particle screen.

B Flexible gas line connectors are not recommended

because they are commonly undersized and restrict
gas flow. Oversize
appliance connector if one must be used.

the diameter of any flexible gas

15

Appliance details

Follow boxed numbers for piping just one 635-ES (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.

Nominal
Iron Length of Black Iron Pipe, Feet
Pipe Internal

Size, Diameter

inches inches 10 20 30 40 50 60 70 80 90 100 125 150 175 200

1/4 0.364 32 22 18 15 14 12 11 11 10 9 8 8 7 6

3/8 0.493 72 49 40 34 30 27 25 23 22 21 18 17 15 14

1/2 0.622 132 92 73 63 56 50 46 43 40 38 34 31 28 26

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

1 1/2 1.610 1600 1100 890 760 670 610 560 530 490 460 410 380 350 320

2 2.067 3050 2100 1650 1450 1270 1150 1050 990 930 870 780 710 650 610

* EHD = Equivalent Hydraulic Diameter. The greater the
value of EHD, the greater the gas capacity of the tubing

.

Maximum Capacity of Semi-Rigid (flexible, non
corrugated) 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

FOR LP GAS

Maximum Capacity 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).

Copper

Outside Length of Tubing, Feet
diameter
Inch 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

Nominal

Iron Pipe

Black Iron Pipe

Size,

Length of Pipe, Feet

Inches

10 20 30 40 50 60 70 80 90 100 125 150

1/2 275 189 152 129 114 103 96 89 83 78 69 63

3/4 567 693 315 267 237 217 196 185 173 162 146 132

1 107 732 590 504 448 409 378 346 322 307 275 252

1 1/4 220 149 121 103 913 834 771 724 677 630 567 511

1 1/2 330 229 185 155 141 127 118 108 102 976 866 787

* EHD = Equivalent Hydraulic Diameter. The greater the
value of EHD, the greater the gas capacity of the tubing.

Tube
size,
inches EHD*

10 20 30 40 50 60

1/2

18 EHD

82 58 47 41 37 34

3/4

23 EHD

161 116 96 83 75 68

1

30 EHD

330 231 188 162 144 131

1 1/4

37 EHD

639 456 374 325 292 267

Length of Flexible Corrugated Stainless Steel Tubing (CSST), Feet

Tube
size
inches EHD*

10 20 30 40 50 60

1/2

18 EHD

129 91 74 64 58 53

3/4

23 EHD

254 183 151 131 118 107

1

30 EHD

521 365 297 256 227 207

1 1/4

37 EHD

971 661 528 449 397 359

Length of Flexible Corrugated Stainless Steel Tubing (CSST), Feet

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.

Fig. 22

16

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Appliance details

i

2.11 Gas line sizing

B It is strongly recommended that the Natural Gas pipe

be Black Iron pipe the entire distance from the
outside meter to the inlet of the gas connection. ¾”
Black Iron pipe up to 20 feet (6.1m) and 1” Black Iron
pipe up to 70 feet (21.34m) distances. Flex line is
NOT recommended, but if used, then oversize the
diameter of the flex pipe, keep the length to a
minimum and try to keep the flex line as straight as
possible.

B It is strongly recommended that the LP Gas pipe be

semi-rigid copper or Black Iron pipe from the outside
regulator to the inlet of the gas connection. For semi­rigid copper piping: 5/8” up to 10 feet (3.05m) and
¾” up to 30 feet (9.14m) distances. For Black Iron
piping: ½” up to 20 feet (6.1m) and ¾” up to 80 feet
(24.38m) distances. Flex line is NOT recommended,
but if used, then oversize the diameter of the flex
pipe, keep the length to a minimum and try to keep
the flex line as straight as possible.

THESE FIGURES ARE FOR GWH-635­ES SUPPLY ONLY, ALL OTHER
APPLIANCES IN THE BUILDING MUST
BE INCLUDED IN THE PIPE SIZING.

2.12 Measuring gas pressure

2.12.1 Connecting Manometer

B Shut off gas.
B Remove front cover and locate inlet gas pressure

measuring point (see Fig. 24).

B Loosen screw inside test point fitting (do not remove)

and connect manometer tube on test point.

2.12.2 Static Pressure Test

B Turn gas supply back on.
B Operate all other gas appliances on same gas piping

system at maximum output.

B Record static gas pressure reading in table 5.

2.12.3 Operating Pressure Test

B ON/OFF switch in position OFF (0).
B Press and hold "Program" (M) button and turn ON/

OFF switch to ON position.

National Fuel Gas Code requires that a sediment trap
(drip leg) be installed on gas appliances not so
equipped. Also, a manual gas shut off valve must be
installed on the gas supply line within close proximity of
the water heater and be visible from the water heater.

Warning: 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 psig.

The water heater must not be piped with gas supply
pressures in excess of 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.
When connections are made, check for gas leaks at all
joints. Apply some soapy water to all gas fittings. Soap
bubbles are a sign of a leak.

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 soapy solution. Never test for gas
leaks using a match or flame.

Fig. 23

B As soon as '188' is displayed, release "Program"

button and the display should read P2.

B Press , until P1 appears.
Note: While in this mode the appliance will run

constantly at maximum power and allow maximum water
flow.

B Turn on high volume of hot water flow (at least 6

gpm) and heater will ignite.
B Record operating gas pressure reading in table 5.
Gas pressures lower than 5" W.C. for Natural Gas or

11" W.C. for LPG will result in insufficient degree rise
to the hot water being used, and must be corrected.
See Gas Connections, chapter 2.10.

Fig. 24 Gas pressure measuring (left tapping)

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17

Appliance details

Static Gas Pressure Reading (see Chapter 2.12)

enter here: ___________________

Operating Gas Pressure Reading (see Chapter 2.12)

enter here: ___________________

Table 5

HIGH ALTITUDE OPERATION

Altitude Natural

0 - 4,000 ft
(0 - 1,219 m)

4,000 ft - 7,000 ft
(1,219 m - 2,134 m)

Above 7,000 ft
(above 2,134 m)

Gas:

no

modification

CO2 adjustment with flue
gas analyzer required See
chapter9 for instructions.

Liquid

Propane:

no

modification

Not approved

For operation at

elevations

above 2,000 ft

(610 m) the

equipment
ratings shall be
reduced at the

rate of 4% for
each 1,000 ft

(305 m) above

sea level

Table 6

2.13 Water connections

When facing the heater, the ¾” cold water inlet is on the
bottom right and the hot water outlet is on the bottom
left. Install the heater centrally in the building if possible
and make hot water piping runs as short as possible.

local codes if more stringent). Never sweat any rigid
piping directly to or beneath the water connections,
damage can occur to the internal water valve from
heating of the pipe. Plastics or other PEX type plumbing
line materials are not suitable for connecting directly to
the water heater. Keep water inlet and outlet pipes to no
less than ¾" (19.05mm) diameter to allow the full flow
capacity.
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 should be installed on both the cold
water supply and hot water outlet lines to facilitate
servicing the heater (see Fig. 26). 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 supplied with the heater
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. 26. 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.

Fig. 25

B THE USE OF A UNION WHEN CONNECTING

BOTH WATER PIPES TO THE INLET AND
OUTLET CONNECTIONS IS RECOMMENDED,
THIS WILL FACILITATE ANY NECESSARY
SERVICING AND REQUIRED CLEANING OF
THE INLET WATER PARTICLE SCREEN.

Although water piping throughout the building may be
other than copper, we recommend that copper,
galvanized or suitably rated stainless steel flex line
piping be used for the water heater connections (follow

18

Fig. 26 Plumbing Connections and Pressure Relief

Valve

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Appliance details

i

2.14 Electrical connections

Warning: For safety reasons,

disconnect the power supply to the
heater before any service or testing is
performed.

Warning: This heater must be
electrically grounded in accordance
with the most recent edition of the
National Electrical Code. NFPA 70. In
Canada, all electrical wiring to the
heater should be in accordance with
local codes and the Canadian Electrical
Code, CSA C22.1 Part 1. Do not rely
on the gas or water piping to ground the
metal parts of the heater.

The GWH-635-ES requires an electrical power supply
from a 120VAC 60Hz circuit and must be properly
grounded.
A means for switching off the 120VAC power supply
must be provided.
The heater is wired as shown in the wiring diagram
(chapter 6, Fig. 37).

2.15 Operating instructions

B Before proceeding with the operation of the heater

make sure that the system is filled with water.

B Turn off power supply to heater.
B Open the cold water inlet supply to the heater fully.
B Open a hot water faucet to permit the water to fill the

heater and the piping and to eliminate the air trapped
in the system.

B Close the hot water faucet after the water flows freely

and all the air has escaped from the system. Turn on
power supply to heater. The water heater is now
ready to operate.

NOTE: A default temperature setting of
122 F will appear on the display screen.

2.16 For your safety read before
operating your water heater

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 is equipped with electronic ignition for
lighting the main burners. When turning the heater on,
follow these instructions exactly.
B. Before operating the unit, set the On/Off switch to
the On ( I ) position.

WHAT TO DO IF YOU SMELL GAS

B Do not try to light any appliance.
B Do not touch any electric switch; do not use any

phone in your building.

B Immediately call your gas supplier from a neighbors

phone. Follow the gas supplier’s instructions.

B If you cannot reach your gas supplier, call the fire

department.

C. Use only your hand to turn the on/off control switch.
Never use tools. Follow these instructions exactly. If
control switch is jammed, close the gas supply and call
a qualified service technician. Attempted forceful repair
may result in a fire or explosion.
D. 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.

2.17 Lighting and operating instructions

B 1. STOP! Read the previous safety information.
B 2. The gas valve must be shut off by putting the ON/

OFF switch to position (0). Wait five (5) minutes to
clear out any gas. If you smell gas, STOP! Follow “B”
in the safety information above. If you do not smell
gas, go to the next step.

B 3. This appliance is equipped with electronic ignition

for lighting the main burners. When turning the
heater on, follow these instructions exactly.

B 4. Set the ON/OFF switch to the (I) position. In this

position, the water heater is ready to use.

B 5. Open a hot water tap.
B 6. The burners will remain on until the hot water tap

is turned off.

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19

Appliance details

i

NOTE: on a first time initial instal­lation or after gas line work has
been done, existence of air in the
gas line will cause ignition delay
when the hot water is turned on.
This will result in an error (EA) on
the units display screen. This is
normal. When this occurs, leave
the hot water running and wait 3-5
seconds, then reset the unit (Fig.
26, pos. 2). Wait for (EA) to disap­pear. The heater will begin to at­tempt ignition again, if the (EA)
reappears then repeat this same
process until all air has been bled
from the gas line.

When the heater is in operation you will hear its power
vent fan and burner operating. Upon turning off the hot
water flow the power vent fan will continue to operate
for up to 60 seconds to exhaust all flue gases. The
power vents fan speed is variable depending on the rate
of hot water used and the burner output.

TO TURN OFF GAS TO APPLIANCE

B Turn off the manual gas shut off on the supply line to

the heater and set the ON/OFF switch to the OFF (0)
position. Note: a manual gas shut off valve is not
supplied with the heater.

20

6 720 607 072

3 Operation instructions

Fig. 27

1 On/Off switch
2 Reset button
3 Program Key
4 Increasing temperature selector
5 Decreasing temperature selector
6 LCD display

Operation instructions

B Press buttons and in order to reach

requested temperature.

3.1 Power

On

B To start the appliance switch the button to position

(I).
LCD display the default temperature - temperature
factory setting 122°F (50°C).

Fig. 28

Off

B To shut down the appliance switch the button to

position (0).

Fig. 29

If the outlet water temperature is set too high, the heater
can produce temperatures that are too hot. A
temperature balance shower valve can automatically
mix in cold water to reduce such hot water temperature.
In the event of any temperature instability with the use
of a temperature balance shower valve, refer to shower
valve manufacturer's instructions for internal adjustment
setting. Adjustments should be made to the hottest
setting in the shower valve. Additionally the temperature
control of the heater can be lowered to produce a more
comfortable hot water temperature.

3.2 Temperature selection

To select water temperature outlet:

6 720 607 072

21

Operation instructions

Hot Water Flow and Temperature with Various Inlet Temperature (lpm/Celsius)

0.00

4.00

8.00

12.00

16.00

20.00

24.00

35 40 45 50 55 60 65

Hot water temperature (ºC)

Hot Water Flow (l/min)

Inlet (ºC) 4 Inlet (ºC) 10 Inlet (ºC) 16 Inlet (ºC) 21

Hot Water Flow and Temperature with Various Inlet Temperature (gpm/Fahrenheit)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

90 100 110 120 130 140 150

Hot water temperature (ºF)

Hot Water Flow (GPM)

Inlet (ºF) 40 Inlet (ºF) 50 Inlet (ºF) 60 Inlet (ºF) 70

Programming the heater to display temperature readings in Celsius is possible, contact BBTNA for instruction.

Setting the water temperature

The desired temperature of the hot water can be adjusted on the front control panel of the heater.
The GWH-635-ES has an electronically controlled gas valve that modulates the burner input in response to both
varying hot water flow rates and/or changes in any incoming and outgoing water temperatures.

Fig. 30 Flow/temperature charts

22

6 720 607 072

3.3 Use of remote control accessory

i

Operation instructions

Fig. 34 Reset button

If the problem persists, contact your installer.

Fig. 31 Remote control

The wireless remote control accessory and the
temperature selector buttons on the front of the water
heater operate identically. Contact your distributor or
BBTNA to order if the remote control accessory is
preferred. Modification of the water heaters interior
control unit (Fig. 29, component 12) is required when
programming the remote control with this heater.

NOTE: up to 6 remote controls can be
programmed for one single water heater,
each with a range distance of 98 ft (30 m).

3.4 Operation

B When a hot water tap is opened, main burner ignites

and LCD displays indication .

Fig. 32

B LCD blinks until selected temperature is reached.

3.5 Reset button

If the LCD shows the error symbol .
See the error code on LCD and consult
“Troubleshooting” section.

3.6 Program button

Program button can be used/programmed in the
appliance and in the remote control.

Programming “Program” function

Programming actions are similar for both controls
(appliance control pad and wireless remote control).

Fig. 35 “Program” key

B Press buttons and to select temperature to

be memorized.

B Hold “Program” button for 3 seconds to save

temperature.

When LCD stops blinking. Temperature is saved on
“Program”.

Using “Program” function

In order to select memorized temperature

B Press “Program” key.

LCD shows pre-memorized temperature, which is now
the hot water selected temperature.

3.7 Locked condition

This condition is only valid for appliances with more
then 1 controller (appliances with remote control).

Fig. 33

After following instructions indicated in
“Troubleshooting” section

B press reset button in order to make the appliance

ready-to-work.

6 720 607 072

Fig. 36 Locked condition

Whenever LCD shows the temperature setting
cannot be adjusted because the appliance is in use by
a user which already selected a different temperature.
Appliance will be automatically unlocked after closing
hot water tap.

23

Maintenance and service

4 Maintenance and service

Warning: Always turn off the electrical

power supply, turn off the manual gas
valve and turn off the manual water
control valves whenever servicing.

The unit should be checked once a year by a gas
technician. If repairs are needed, the repairs should be
done by a gas technician

To remove front cover

B Remove plastic decals on front panel (Page 5, Fig.

3).

B Loosen the two Philips head screws located behind

decals.

B Lift front cover panel upward and remove.

Systems and parts that should be checked at
least once a year

Reference diagrams on pages 29 and 30.

• Venting system

• Burners -see page 29 for observation window

• Manual operation of the pressure relief valve to insure
correct operation

• Periodic cleaning of the water filter screen, see Fig.
25, chapter 2.13.

• Flushing the heat exchanger with a descaling
solution if mineral build up is evident. Scale build up
will shorten the life of the water heater, descale heat
exchanger thoroughly and repeat annually depending
on mineral content of ground water.

5 Troubleshooting

Introduction

The GWH-635-ES burner is activated by a water flow
valve. Numerous water related problems can cause this
water valve to malfunction such as: Insufficient water
flow volume to activate the burners at its minimum flow
requirement; Dirt in the water flow valve causing it to
malfunction; Sediment build-up in faucet aerators, or
shower heads; Uneven pressures between cold and hot
(with single lever mix valves); and Plumbing crossovers.
These water flow related problems can cause the
heater to deliver less than its full output, or to fail to
ignite or to shut down completely.
Problems stated below in upper case and in bold face
should be investigated when there is a problem with the
performance of the water heater but there is NO error
code on the heater's LCD display or wireless remote
control.
Any failures that result in a displayed error code are
referenced on page 26. A Functional Scheme of the
GWH-635-ES is detailed on page 28. If there is a
problem with the installation, venting or operation of the

unit, the heater will communicate the source by these
error codes.

BURNERS DO NOT IGNITE WHEN HOT WATER IS
TURNED ON

• Cold incoming water connection made to

wrong side of heater

Make sure cold water inlet connection is plumbed to
the right side of heater when facing unit

• Water flow rate at hot water tap is too low
A minimum of 0.8 gallon/minute (3 l/m) is required to
activate the heater

• Cold water inlet filter screen is dirty
Remove water inlet filter screen and clean. The
screen is located at the inlet connection to the water
heater, disconnecting the main cold supply line at the
heater is required. Check and clean faucet aerator
screens too.

• Crossover in plumbing
The heater activates when there is sufficient water
flow through its water valve, a minimum of 0.8 gallon/
minute (3 l/m) is required. If there is a crossover in the
plumbing, the necessary hot water flow rate through
the unit may not be reached, even though the flow at
the hot water tap is sufficient. A plumbing crossover
can be caused by a failed washer at a single lever
faucet, incorrect plumbing or a faulty mixing valve in
the piping. The crossover will create a back pressure
on the water heater and prevent an adequate flow of
water through it. To confirm there is no crossover in
the plumbing, shut off the cold water supply feed to
the water heater. Individually open each of the hot
water taps. There should be no water flowing under
a constant pressure. If there is a constant flow of
water then the plumbing crossover must be
corrected before the heater can operate properly.

WATER IS TOO HOT

• Temperature selection too high
Lower temperature adjustment on heater or wireless
remote control accessory, see chapter 3.2.

WATER IS NOT HOT ENOUGH

• Temperature selection too low
Increase temperature adjustment on heater or
wireless remote control accessory, see chapter 3.2

• Btu input is too low due to inadequate gas line

sizing

See specifications in chapter 2.10 - 2.12. The
GWH-635-ES requires adequate gas pressure to
reach desired temperatures, to compensate for
inadequate gas supply or lack of gas pressure the
GWH-635-ES will effectively reach the selected
output temperature by reducing the hot water flow
rate. Its motorized water valve makes this adjustment

24

6 720 607 072

Troubleshooting

• Cold water is mixing with the hot water outlet

(crossover)

Test by following 4th bullet under BURNERS DO
NOT IGNITE WHEN HOT WATER IS TURNED ON.

LOW WATER FLOW/PRESSURE

• Too many hot water applications are being

used simultaneously or too much flow is being
demanded

The GWH-635-ES will effectively support two 2.0-

2.5 gpm shower heads simultaneously or multiple
sink applications. Greater draws will result in
increased pressure drop and reduced flow at taps.
See flow/temperature chart on page 22.

• Btu input is too low due to inadequate gas line

sizing

See specifications in chapter 2.10 - 2.12. The
GWH-635-ES requires adequate gas pressure to
reach expected temperatures and flow rates, to
compensate for inadequate gas supply or lack of gas
pressure the GWH-635-ES will effectively reach the
selected output temperature, but only by reducing
the hot water flow rate. Its motorized water valve
makes this adjustment. Proper gas pressure will
need to be delivered before the motorized water
valve will allow greater flow rates through it. Lowering
the set temperature will also allow increased water
flow rate through the motorized water valve. See
flow/temperature chart on page 22.

• Cold water inlet filter screen is dirty
Remove water inlet filter screen and clean. The
screen is located at the inlet connection to the water
heater, disconnecting the main cold supply line at the
heater is required. Check and clean faucet aerator
screens too.

Adjustments should be made to the hottest setting in
the shower valve. Additionally the temperature
control of the heater can be lowered to produce a
more comfortable hot water temperature.

• Inlet water pressure is erratic due to

fluctuating supply water pressure

For installation on a private well system with the use
of a pressure tank, the lowest pressure range setting
recommended is 30-50 psi (2.07-3.45 bar). The use
of a pressure reducing valve after the pressure tank
is also an effective way to maintain a constant water
pressure to the water heater. Watts brand 25AUB­¾” or N35B-¾” pressure relief valves or equivalent
are suggested.

NOISY BURNER / HEATER DURING OPERATION

• CO2 range is out of adjustment. The cover must be
in place to confirm CO2 readings. Operating with the
cover removed may cause a noisy or unstable burner.
See Chapter 9, CO2 adjustments can only be done
by a certified gas technician with a calibrated CO
analyzer.

2

HOT WATER TEMPERATURE FLUCTUATES /
UNIT DEACTIVATED

• Unbalanced pressure in water lines
Any restriction caused by the water heater in the hot
water system can result in uneven pressures
between the cold and the hot. In such cases when
mixing cold water at the tap (manually or
automatically through a mix-type shower valve) the
lower hot water pressure may be overpowered by the
higher cold water pressure in the building and cause
the hot water flow rate to fall below the minimum rate
required. A pressure balance valve will help to
resolve this symptom.

• Temperature balance valves
If the outlet water temperature is set too high, the
heater can produce temperatures that are too hot. A
temperature balance shower valve can automatically
mix in cold water to reduce such hot water
temperature. In the event of any temperature
instability with the use of a temperature balance
shower valve, refer to shower valve manufacturer's
instructions for internal adjustment setting.

6 720 607 072

25

Troubleshooting

Display Cause Solution

E9 Temperature limiter opened circuit

(overheat). Trips at 220F (104C).

EA No ionization during safety time (safety time

out).
Note: appliance makes 3 ignition attempts
before entering error mode “EA”.

EC The ionization signal momentarily

disappeared more then 5 times in less then
30 seconds.

FA Leakage error (gas valves do not close gas

circuit).

F7 Ionization error (flame sensing at stand-by). Check control unit.*

E0 Internal software/hardware failure. Check control unit.*

A7 Hot water temperature sensor/receiver

defect (from control unit).

A9 Hot water temperature sensor/receiver mis-

assembled (from control unit).

Note: if display shows “A9” flashing, the
appliance can be operated normally, but
performance may be affected.

Check connections.*
Check heat exchanger condition.*

Check gas pressure.*
Check that gas is not diluted with air, as a result
from recent gas pipeline rework.*.
Check if vent terminal is blocked (especially when
the appliance starts up for some seconds and then
looses ionization signal).*
Check ionization electrode.*
Check for a proper ground.*

Check gas valve and control unit.*

Check water temperature sensor/receiver and
connections.*
Check room area temperature where heater is
located, it must be above 36°F (2°C)

Close water tap and allow 30 seconds for purging
time.
Open water tap and wait for 2 minutes to see if A9
message is deleted from the display.
Check that the water temperature sensor/receiver is
properly assembled in the water pipe.*
Check that the water temperature sensor/receiver is
in proper condition.*

C1 FAN rotation too low at start-up (from

control unit).

C6 FAN rotation too low at operation (from

control unit).

C7 No rotational speed sensor signal from FAN Check fan and connections.*

CA Water flow signal over specified maximum

value

E2 Inlet temperature sensor fault Check water temperature sensor/receiver and

A2 Overheat protection fault Check connections to the overheat protection.*

Check supply voltage.*
Check fan and connections.*
Check control unit.*
Check if vent terminal is blocked or if vent terminal is
according with
Check CO2 levels (see chapter9).*

Check supply voltage.*
Check fan and connections.*
Check control unit.*
Check if vent terminal is according with

chapter 2.9

Check control unit.*
Check CO2 levels (see chapter9).*

Check water valve and flow sensor.*

connections.*
Check room area temperature where heater is
located, it must be above 36°F (2°C)

Check sensor continuity.*
Check heat exchanger sealings and walls.*

chapter 2.9

.*

. *

Table 7

26

* By installer or service technician only.

6 720 607 072

6 Electrical diagram

Electrical diagram

Fig. 37 Electrical scheme

1 Intlet water temperature sensor
2 Ionization sensor
3 Water flow sensor
4 Over heat protection
5 Temperature limiter
6 Gas valve
7 Fan
8 Water valve
9 AC Plug
10 Ignition electrode
11 Display PCB
12 ON/OFF switch
13 Fuse T 2,5A
14 Fuse T 3,15A
15 Terminal block
16 Ground post
17 Outlet water temperature sensor

6 720 607 072

27

GWH-635-ES Functional scheme

7 GWH-635-ES Functional scheme

Fig. 38 Functional scheme

28

6 720 607 072

Interior components diagram and parts list

8 Interior components diagram and parts list

8.1 Interior components

Fig. 39 Components

1 Cover
2 On/Off switch
3 Reset button
4 LCD display
5 Program button
6 Temperature switches
7 Flue gas collector
8 Mixer
9 Heat exchanger
10 Observation window
11 Inlet air duct
12 Control unit
13 Exhaust fan
14 Water valve
15 Gas valve

6 720 607 072

Fig. 40 Appliance overview

29

Interior components diagram and parts list

8.2 Components diagram

Fig. 41 Components Diagram

30

6 720 607 072

Interior components diagram and parts list

8.3 Parts list

Item Description Reference

1 Front cover 8 705 421 837

2 Shield 8 705 506 661

3 Heat exchanger 8 705 406 285

4 Heat exchanger top gasket 8 704 701 052

5 Clip 8 716 102 607

6 Heat exchanger bottom gasket 8 704 701 054

7 O-ring 8 700 205 147

8 Temperature sensor 8 700 400 015

9 Washer 1/2" 8 710 103 045

10 Wireform spring 8 714 606 002

11 Air inlet duct 8 705 700 097

12 Water filter 8 700 507 001

13 O-ring 8 700 205 134

14 Water valve with engine 8 708 505 016

15 Main burner 8 708 120 515

16 Fan / Burner gasket 8 704 701 050

17 Set of electrodes 8 708 107 020

18 Exhaust Fan 8 707 204 039

19 Gas / Air Mixer 8 705 700 115

20 Mixer / Fan gasket 8 704 701 059

21 Gas valve washer 8 704 701 062

22 Gas valve 8 707 021 019

23 Gas valve washer 8 700 103 014

24 Remote control 8 707 207 153

25 Control unit 8 707 207 133

26 Ignition cable 8 704 401 220

27 Cables / 24V 8 704 401 214

28 Cables 8 704 401 239

29 Power supply cord 8 704 401 221

30 Overheat cutoff fuse 8 700 400 019

31 Flue gas exhaust accessory 8 705 504 137

32 Combustion air inlet accessory 8 705 504 115

33 Flue gas collector 8 705 700 100

34 Flue gas collector collar 8 705 700 114

35 Cold water pipe 8 700 715 156

36 Hot water pipe 8 700 715 155

37 Air inlet screen 8 700 507 069

38 Crossover tube 8 700 715 247

39 Overheat sensor (ECO) 8 707 206 204

40 Clip - Heat exchanger 8 701 201 028

41 Clip - Over heat fuse 8 701 201 024

42 Gasket Exhaust 8 700 103 710

43 Gasket Set Combustion Chamber 8 704 701 046

44 O-ring air duct 8 700 205 149

Table 8

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31

Special adjustment for measuring and adjusting CO2 levels

9 Special adjustment for measuring and adjusting CO2 levels

The CO2 can only be adjusted by a certified gas
technician with a calibrated CO2 analyzer.

Caution: One factor that may affect

CO2 levels is improper gas pressure.
Please see Chapter 2.12 for the
procedure to measure gas pressure
and record your findings below:

Static Gas Pressure: “ WC

P1 Operating Pressure: “ WC

The P1 minimum operating pressure is 5" WC for
Natural Gas and 11"WC for Propane. Do not proceed
in adjusting CO2 until pressure has been verified to be
at or above these levels, but not to exceed 14” WC.

A. Once Pressure is good

B Turn ON/OFF switch to the OFF (O) position.
B Remove brass flat head screw on the exhaust collar

as seen in Fig. 42.

B Insert CO2 analyzer probe into the measuring port.

The tip of the probe should be in the center of the flue
pipe (approx 1.5" inserted).

B. Measuring CO2 (Cover Installed):

B Open hot water taps to achieve a flow rate of at least

4 gallons per minute. (1 tub and 2 sinks should be
sufficient).

B Record the CO2 reading in P2 below. (Analyzer

reading may take several minutes to stabilize).

B Press the ‘+’ button until P1 appears. Unit will ramp

up to high fire and the flow should increase.
B Record the CO2 reading in P1 below.
P2 CO2 Reading: % CO

P1 CO2 Reading: % CO

2

2

Compare your readings to those found in table 9 under
the “With Front Cover” column. If CO2 readings are off
make adjustments as outlined below.

Note: The “Without Front Cover” column give
approximate values with the cover off to ease the
adjustment process. Final readings should be taken
with the cover on.

C. Adjusting CO2:
Note: P1 adjustment will change the P2 reading.

Confirm the P1 value BEFORE adjusting the P2 level.

Fig. 42

B While holding the Program (M) button, move the ON/

OFF switch to ON (I) position (see Fig. 43). As soon
as ‘188’ flashes on the display, release the Program
button. The display should now read P2.

1. P1 CO2 level off:
B Loosen yellow painted Philips screw (1) and cover

should rotate down (2) revealing a brass slotted

screw. Fig. 44.
B Adjusting the slotted screw counter clockwise will

raise P1 CO2 levels and clockwise will lower P1

CO2 levels. Adjustments to the slotted screw will

also change P2 CO2 levels.

2. P2 CO2 level off:
B Remove yellow painted #40 Torx cover from the front

of the gas valve. (Fig. 45) A plastic #40 Torx screw

will be revealed.
B Adjusting the plastic #40 Torx screw counter

clockwise will lower P2 CO2 levels and clockwise

will raise P2 CO2 levels.

Note: These screw adjustment are very sensitive and
may take several minutes to stabilize.

3. Verify both P1 and P2 are within the ranges specified
in table 1 under the “With Front Cover” column. Repeat
steps 1 and 2 as necesssary until CO2 values are within
the specified ranges.

Fig. 43

32

6 720 607 072

Special adjustment for measuring and adjusting CO2 levels

D. Returning to Service:

1. Return slotted cover to original position.

2. Reinstall Torx cover.

3. Remove CO2 analyzer probe and reinstall flathead
screw in exhaust collar.

4. Turn ON/OFF switch to the OFF (O) position and
then back to the ON (I) position.

5. Heater is ready for normal operation.

Without Front

Cover

Nat. Gas Nat. Gas

max. input P1 9.1 ± 0.1 % 9.7 ± 0.1 %

min. input P2 9.4 ± 0.1 % 9.7 ± 0.1 %

LP Gas LP Gas

max. input P1 10.1 ± 0.1 % 10.7 ± 0.1 %

min. input P2 10.4 ± 0.1 % 10.7 ± 0.1 %

* Final reading must be confirmed with the front cover
on, CO2 levels increase when the cover is installed.

With Front

Cover

Table 9

Final Readings

P2 CO2 Reading: % CO

P1 CO2 Reading: % CO

2

2

Fig. 45

Fig. 44

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33

Protecting the environment

10 Protecting the environment

Packing

The packing box may be fully recycled as confirmed by
the recycling symbol .

Components

Many parts in the heater can be fully recycled in the end
of the product life. Contact your city authorities for
information about the disposal of recyclable products.

Saving water resources:

B Make sure you close all the taps after any use. Avoid

leaving the taps dripping. Repair any leaking tap.

B Whenever possible use taps with built-in water flow

limiters. They will give you the same comfort level
while saving water.

B Define the temperature you want, in the appliance or

with the remote control. This way you have the
precise water flow needed (mixing cold water to
regulate temperature will increase the water flow with
consequent waste of water).

For increased safety shut off the appliance from
the main water supply if your are staying away
from home for a considerable time.
At below freezing temperatures, disconnect the
plumbing connections to the heater and allow
the heater to drain.
To prevent any freeze damage, introduce short
bursts of compressed air (20-40 psi) through
these connections to remove the residual water
in the horizontal pipes and water valve.

34

6 720 607 072

11 Fifteen Year Limited Warranty

i

Fifteen Year Limited Warranty

General

BOSCH PRO water heaters are warranted by the
Manufacturer (BOSCH) through BBT North America.
BBT North America (BBTNA) will furnish a replacement
heat exchanger and will furnish a replacement of any
other part which fails in normal use and service within
the applicable periods specified below, in accordance
with the terms of this warranty. The BBTNA
replacement will be warranted for the unexpired portion
of the original warranty. This warranty will be valid only
for water heaters in possession of the original purchaser
as recorded on the warranty card.

The Heat Exchanger

If the heat exchanger fails within fifteen (15) years after
the original installation and operation, BBTNA will
furnish a replacement heat exchanger. However, if the
water heater is installed in other than a single family
dwelling, this heat exchanger warranty is limited to two
(2) years from date of original installation and operation.

Exceptions

This warranty will not apply:

• 1. to defects or malfunctions resulting from failure to
properly install, operate or maintain the unit in
accordance with the printed instructions provided;

• 2. to damage or abuse, accident, neglect or freezing
and other acts of nature;

• 3. to damage resulting from operation with either the
flame sensor rod or overheat sensor removed;

• 4. to failure of the heat exchanger resulting from the
operation of the water heater in a corrosive
atmosphere or at water temperatures exceeding the
maximum rating, or if the water heater is not supplied
with potable water;

• 5. to defects or damage cause by any attachment
or modification, including any energy-saving device.

All Other Parts

If any other part fails within three (3) years after original
installation and operation, BBTNA will furnish a
replacement part free of charge.

Shipping costs

In addition to supplying the replacement part(s),
BBTNA will provide ground service delivery for these
parts. Expedited or upgraded shipping will be charged
to the customer.

of the original water heater or a replaced water heater.
Certain service labor allowances are available to PHCC
member contractors, dependent on prior authorization
by BBTNA.

NOTE: the water heater must be free of
damaging scale deposits and not subject
to gas pressures greater than those
shown on the rating plate, which must not
be altered, defaced or removed.

How to Make a Claim

Any claim for warranty parts should be made to your
local dealer, distributor or to BBTNA. If BBTNA, please
contact the Technical Support Department:

BBT NORTH AMERICA
Bosch Group
340 Mad River Park

Waitsfield, VT 05673
Phone [phone]
www.boschpro.com

In most cases, the dealer or distributor will be able to
promptly honor your claim and subsequently notify
BBTNA. However, all replacements are made subject to
validation by BBTNA of in-warranty coverage. The
damaged or defective item must be made available in
exchange for the replacement.

Miscellaneous

No one is authorized to make any other warranties on
behalf of BBTNA. It is expressly understood that the
replacement warranty of BBTNA shall be in lieu of any
and all other warranties, express or implied, including
warranties of merchantability or fitness for a particular
use or purpose, and further that BBTNA shall not be
liable for any loss or damage directly or indirectly arising
from the use of the hot water heater, or for any
consequential damages arising from such use
(including damages from water leakage). BBTNA sole
liability with respect to any defect shall be for the
replacement of the defective part(s). Some states do
not allow such limitations and exclusions, so the above
may not apply to you.
This warranty gives specific legal rights. You may also
have other rights which vary from state to state.

Service Labor Costs

This warranty does not cover any labor costs
associated with service, removal or re-installation of
part(s). All such costs must be borne by the Purchaser.
Additionally, this warranty does not cover any labor
costs associated with service, removal or re-installation

6 720 607 072

35

Installer Checklist, to be performed by installer upon installation

Serial Number ___ ___ ___ ___ ___ ___ ___ ___

(8 digit serial number is located on rating plate on right side panel)

Gas Pressure Reading* Static__________ Operating__________

Building Water Pressure __________ Range if on Well system __________

Installing Company _____________________________________________

Installer name _____________________________________________

Address _____________________________________________

Phone _____________________________________________

* See Chapter 2.12 and gas pressure table (to be filled out by installer)

Installation manual should be left with the owner after the installation is tested and completed

Replacement Parts available from:

BBT NORTH AMERICA
Bosch Group

Bosch Water Heating
340 Mad River Park
Waitsfield, VT 05673

VULCANO Termodomésticos S.A.

Estrada de Cacia

3801 - 856 Aveiro - PORTUGAL

Phone [phone]
Fax [phone]
www.boschpro.com
[e-mail]

Recycled paper © 2005 BBT NORTH AMERICA,

Waitsfield, VT all rights reserved