Bosch GWH C 920 ES User manual

GWH C 920 ES/ESC
INDOOR RESIDENTIAL AND COMMERCIAL MODELS
Temperature Modulated with Electronic Ignition
Suitable for heating potable water - Not approved for space heating purposes
(Intended for variable flow applications)
GWH C 920 ES/ESC - Natural Gas
GWH C 920 ES/ESC - Liquefied Petroleum (LP) Gas
6 720 608 836 (2009/05) US
Warning: If the information in this manual is not
followed exactly, a fire or explosion may result
causing property damage, personal injury or death.
Do not store or use gasoline or other flammable
vapors and liquids in the vicinity of this or any other
appliance.
Improper installation, adjustment, alteration,
service or maintenance can cause injury or
property damage. Refer to this manual. For
assistance or additional information consult a
qualified installer, service agency or the gas
supplier.
In the Commonwealth of Massachusetts this
product must be installed by a licensed plumber or
gas fitter.
Upon completion of the installation, these
instructions should be handed to the user of the
appliance for future reference.
What to do if you smell gas
• Close gas valve. Open windows.
• Do not try to light any appliance.
• Do not touch any electrical switch; do not use any
phone in your building.
• Immediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
• If you cannot reach your gas supplier, call the fire
department.
• Installation and service must be performed by a
qualified installer, service agency or the gas supplier.

6 720 608 836
2
Index
Index
1 Warning 3
2 Appliance details 4
2.1 Features 4
2.2 GWH C 920 ES and GWH C 920 ESC
Specifications (Technical data) 5
2.3 Unpacking the tankless water heater 6
2.4 General rules to follow for safe operation 7
2.5 Dimensions and minimum installation
clearances 8
3 Installation instructions 9
3.1 Specialized tools 9
3.2 Introduction 9
3.3 Venting 9
3.4 Combustion air requirements 20
3.5 Proper location for installing your heater 21
3.6 Heater placement and clearances 21
3.7 Mounting installation 21
3.8 Gas piping & connections 22
3.9 Water connections 25
3.10 Water quality 26
3.11 Domestic hot water recirculation 27
3.12 Filling the condensate trap 28
3.13 Measuring gas pressure 29
4 Electrical connections 30
4.1 Electrical power supply 30
4.2 Position of the fuses in control unit 30
5 Operation instructions 31
5.1 Description of LCD Display 31
5.2 For your safety read before operating
your water heater 32
5.3 Power 32
5.4 Temperature selection 32
5.5 Use of optional remote control accessory
(part no. TSTAT2) 33
5.6 Operation 33
5.7 Reset button 33
5.8 Program button 33
5.9 Locked condition 34
6 Maintenance and service 34
6.1 Annual maintenance 34
6.2 Winterizing for seasonal use 35
6.3 Mineral scale build-up 35
6.4 Condensing heat exchanger unit 36
6.5 Adjusting CO2 36
6.6 Program values 39
6.7 Control unit diagnostics 40
7 Troubleshooting 41
7.1 Introduction 41
7.2 Burner does not ignite when hot water
is turned on 41
7.3 Water is too hot 41
7.4 Water is not hot enough 41
7.5 Low water flow/pressure 42
7.6 Hot water temperature fluctuates at tap 42
7.7 Noisy burner/heater during operation 42
8 Error codes 44
8.1 Error code diagnostics 44
9 Electrical diagram 48
10 Sensor resistance charts 49
11 Functional scheme 51
12 Interior components diagram
and parts list 52
12.1 Interior components 52
12.2 Components diagram 54
13 Protecting the environment 61
14 Limited Warranty 62
14.1 Limited warranty for GWH C 920 ES
residential model 62
14.2 Limited warranty for GWH C 920 ESC
commercial model 63

6 720 608 836
Warning
3
1 Warning
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 to
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.
Warning: Exhaust gas must be vented
to outside using approved vent material
See table 2, page 10 (For Canada use
only PVC ULC S636). 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. Approved vent terminators must
be used when penetrating to the
outside.
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, unplug power supply cord from
outlet. Failure to do so could result in
severe personal injury or death.
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.
Warning: The appliance should be
located in an area where water leakage
of the heat exchanger, piping 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
recommended that a 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 that
the minimum value listed is for the
purposes of input adjustment.
Warning: 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.
Warning:
BEvery time there is a demand for hot
water the tankless must recognized the
activation flow, activate the burners and
raise the temperature to the set
temperature.
BThe time to reach set temperature
depends upon the inlet temperature, the
distance to the tap and the water flow.
BUse patterns with short on cycles may
not give the tankless the time to reach
the desired temperature. Examples are
commercial kitchen sprayers and some
dishwashers with short cycles.
BIn such applications a small buffer tank
may be needed to improve performance.
Contact Bosch Water Heating for
additional information.
Warning: Keep the appliance area
clear of combustible materials, gasoline
and other flammable vapors and liquids.

6 720 608 836
4
Appliance details
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.
Fig. 1
2 Appliance details
2.1 Features
Residential/commercial models
• GWH C 920 ES residential model
– maximum temperature 140° F
• GWH C 920 ESC commercial model
– maximum temperature 180° F
Parts
• Key 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.
High quality materials for long working life
• Copper heat exchanger
• High efficiency Ceramat Burner
• Compact space saver: mounts on a wall with
supplied bracket.
Features
• Easily removable one-piece cover
• LCD Display with backlight
• On/Off and Temperature control buttons
• Reset button
• Program button (Selectable temperature default)
• Error codes for easy diagnostics and repair
• Real-time diagnostics for troubleshooting/informa-
tional purposes.
Accessories (Bosch part #)
• Optional wireless remote control to operate with the
appliance (TSTAT2)
• Cascading kit (TLINK)
• Outdoor kit (PTOK)
• External water filter (part # 8 703 305 356)
• Concentric termination kit (BWH60L46)
• Freeze prevention kit (7 709 003 665).
Warning: Do not obstruct the flow of
combustion and ventilation air.
Warning: When manually operating the
relief valve, precautions must be taken
prior to operating the relief valve to avoid
contact with hot water coming out of the
relief valve and to prevent water
damage.
Caution: Label all wires prior to
disconnection when servicing controls.
Wiring errors can cause improper and
dangerous operation.
Verify proper operation after servicing.
Warning: If a relief valve discharges pe-
riodically, this may be due to thermal ex-
pansion in a closed water supply
system. Contact the water supplier or
local plumbing inspector on how to cor-
rect this situation. Do not plug the relief
valve.
HOT
BURN
D A N G E R
Water temperature over 125°F can
cause severe burns instantly or
death from scalds.
Children, disabled and elderly are
at highest risk of being scalded.
See instruction manual before
setting temperature at water
heater.
Feel water before bathing or
showering.
i
BOSCH is constantly improving its
products, therefore specifications are
subject to change without prior notice.

6 720 608 836
Appliance details
5
2.2 GWH C 920 ES and GWH C 920 ESC
Specifications (Technical data)
Approved in US/Canada
Capacity
Maximum flow rate: 9.2 GPM (35 l/min) at a 45°F
(25°C) rise. (with sufficient water pressure)
Maximum output
210,000 Btu/h (61.5 kW)
Maximum input
225,000 Btu/h (65.9 kW)
Efficiency in %
Thermal efficiency > 94%
Minimum Input
25,000 Btu/h (7.3 kW)
Temperature Control
GWH C 920 ES:
• Selection range: 100°F (38°C) - 140°F (60°C).
GWH C 920 ESC:
• Selection range: 100°F (38°C) - 180°F (82°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: 8" - 13" water column
• Natural Gas: 3.5" - 10.5" water column.
* To measure Gas Pressure, see Measuring Gas
Pressure, chapter 3.13, page 29.
Water
• Hot water connection (inches) - ¾"
• Cold water connection (inches) - ¾"
• Water valve material: Polymer (PPS) (Polypropylene
Sulfid)
• Minimum water flow: 0.65 gallon/minute (2.5 l/m)
Note: Activation varies with inlet water temperatures
from 0.65 - 1.6 gallon/minute (2.5 - 6.1 l/m).
• Minimum recommended water pressure: 30 PSI
(2.07 bar)
• Minimum well pressure 40 psi, see page 25.
• Connections:
– Bottom of heater
Combustion
• NOx ≤55 ppm
• CO ≤290 ppm (measured)
• CO
2
level set from factory, see chapter 6.5, page 37.
Dimensions
• Depth (in): 11¼" (286 mm)
• Width (in): 17
7
/
8
" (452 mm)
• Height (in): 30½" (775 mm)
• Weight: 88 pounds (40 kg).
Gas types
Natural Gas.
LP Gas.
Voltage
120 V AC (60 Hz) nominal
Amperage
Idle - 40 mA
Operation - ≤2.5 A
Noise
45 - 65 db (A)
Safety devices
• Flame failure device (ionization flame rod sensor)
• Pressure relief valve (supplied with heater)
• Overheat prevention (temperature limiter/ECO)
• Outlet temperature sensor
• Backflow temperature sensor
• Exhaust gas temperature sensor.
Water protection
IP X4 (protection against water drops)
i
If appliance is installed at elevations above
2000ft, refer to table 12, page 18.

6 720 608 836
6
Appliance details
2.3 Unpacking the tankless water
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.
Fig. 2 Rating plate
ASerial number
BType of gas
The box includes:
• Tankless water heater
• Pressure relief valve (150 psi / 500,000 Btu rating)
• Bracket for wall hanging the heater
• Exhaust vent adaptor (with 4 screws and gasket
provided)
• Combustion air inlet adaptor (with 3 screws and gas-
ket provided)
• Installation manual (manual can be downloaded from
www.boschpro.com)
• Product registration card.
Please complete and return the enclosed product
registration card.
The tankless water heater is not approved or
designed for:
•Manufactured (mobile) homes, boats or any
mobile installation. (Modular homes are
acceptable for installation).
•Use above 8000 ft A.S.L. altitude (see page 18).
•Outdoor installation without installation of
Outdoor kit (PTOK).
• Applications where inlet water temperature is
higher than 140°F (60°C). A thermostatic
mixing valve must be installed before the
appliance.
• Space heating purposes.
To remove front cover
BLoosen the two Philips head screws located on
bottom rear of cover (see Fig. 3).
Fig. 3 Loosen the two screws
BLift front cover upward and remove.
Fig. 4 Remove the front cover
To remove combustion cover (service only;
unplug appliance before removing cover)
BOpen the four clips and remove the combustion
cover (see Fig. 5).
Fig. 5 Remove the combustion cover

6 720 608 836
Appliance details
7
2.4 General rules to follow for safe
operation
B1. You must follow these instructions when you
install your heater. In the United States: The
installation must conform with local codes or, in the
absence of local codes, the National Fuel Gas Code
ANSI Z223.1/NFPA 54.
In Canada: The Installation must conform with CSA
B149.(1,2) INSTALLATION CODES and /or local
installation codes.
B2. Carefully plan where to install the heater. Correct
combustion air supply and vent pipe installation are
very important. If not installed correctly, fatal
accidents can occur, such as carbon monoxide
poisoning or fire.
B3. 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 3.3 (page 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 Fuel
Gas Code does not allow UNSEALED gas fired
water heater installations in bathrooms,
bedrooms or any occupied rooms normally
kept closed. See chapter 3.4 (page 20).
B4. You must correctly vent your heater. See
chapter 3.3 (page 9) on VENTING.
B5. 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).
B6. Keep water heater area clear and free from
combustibles and flammable liquids. Do not locate
the heater over any material which might burn.
B7. Correct gas pressure is critical for the proper
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. See
chapter 3.8 (page 22).
B8. 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 but must
be field installed.
B9. 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.
B10. Failure to install heater correctly may lead to
unsafe operation and void the warranty.
B11. Water temperatures over 125°F can cause
severe burns instantly. If the outlet temperature is set
above 125°F, a thermostatically controlled mixing
valve or temperature limiting valve should be
considered to reduce the risk of scalding. Contact a
licensed plumber or the local plumbing authority for
further information.

6 720 608 836
8
Appliance details
2.5 Dimensions and minimum installation clearances
Fig. 6 Dimensions
1On/Off button
2Reset button
3Program button
4Power ON or stand-by LED
5LCD display
6Up button
7Down button
Fig. 7 Minimum clearances
Note: For servicing access, a 2 foot clearance is
recommended to the front cover.
6720608000-03.2AL
6
4
Model GWH C 920 ES
TOP (A) 12 "
FRONT (B) 1 "
BACK 0 "
SIDES 1 "
FLOOR (C) 12 "
Table 1 Minimum clearances

6 720 608 836
Installation instructions
9
3 Installation instructions
3.1 Specialized tools
The following specialized tools may be required for
installation:
• Manometer
• Multi-meter
• Combustion Gas Analyzer.
3.2 Introduction
Please follow these instructions. Failure to follow
instructions may result in:
BDamage or injury.
BImproper operation.
BLoss of warranty.
3.3 Venting
Warning:
The water heater must be installed by a
qualified installer in accordance with these
instructions. If improperly installed, a
hazardous condition such as explosion or
carbon monoxide poisoning could result.
Bosch Thermotechnology Corp. is not
responsible for improperly installed
appliances.
i
Common installation practice is to
first determine the venting/
combustion air point of termination,
then design the piping layout back to
the heater.
Warning:
BDo not reduce the exhaust or
combustion air vent pipe sizes.
BDo not common vent with any other
vented appliance or stove.
BDo not use Type-B vent as the actual
exhuast vent system for the appliance.
Warning: Failure to vent the exhaust
gases to the outside (see Table 2 for
proper material) may result in
dangerous flue gases filling the
structure in which it is installed.
Warning: In areas where outside
temperatures routinely come close to
freezing, sealed combustion operation
is required. Concentric termination or
separate terminations for combustion
and vent, must be installed on the same
wall or roof surface; however, never
facing the direction of prevailing winds.
Failure to do so may result in heat
exchanger freezing and bursting. This
failure is not covered under the
manufacturer's warranty.
Warning: Protect the exhaust and inlet
from leaves and debris by installing a
screen on the end of the terminator.
¼" mesh minimum opening
recommended on screen.

6 720 608 836
10
Installation instructions
3.3.1 Vent material
All combustion air and vent pipe materials and fittings
must comply with the following:
For specific questions concerning vent material,
specifications, usage or installation, please
contact the vent manufacturer directly.
All vent connections must be glued, except for the
exhaust accessory (see section 3.3.4) which is
screwed into place on the top of the appliance. Slide
the vent pipe into the exhaust accessory. The exhaust
pipe must be properly supported and must be pitched
a minimum of a ¼ inch per foot back to the appliance.
This allows the condensate to drain properly.
An optional concentric vent/air intake termination can
be used for the installation of a vertical or horizontal
venting system. (see Fig. 8).
The concentric vent/air intake body can be ordered
from your local wholesaler. (Part# BWH60L46).
The appliance can also be installed with separate air
intake and exhaust piping (see Fig. 11, Fig. 17 and Fig.
18, page 16).
Fig. 8 Concentric vent kit example
Item Material United States Canada
Vent or
air pipe
and
fitting
PVC schedule 40 ANSI/ASTM D1785
CSA or ULC
certified only
(ULC-S636)
PVC-DWV ANSI/ASTM D2665
CPVC schedule 40 ANSI/ASTM F441
ABS-DWV schedule 40 ANSI/ASTM D2661
Pipe
cement /
primer
PVC ANSI/ASTM D2564
CPVC ANSI/ASTM F493
ABS ANSI/ASTM D2235
Table 2 Approved vent material
i
Do not use cellular foam core pipe.
Description Length
Kit part no. and
quantity
BWH60L46
3- In. Rain Cap N/A 1
4- In. Diameter
SDR-26 Pipe 24 In. long 1
3- In. Y
Concentric Fitting N/A 1
2- ½ In. Diameter
SDR-26 Pipe 37-1/8 in. long 1
Table 3 Concentric vent part breakdown
6720608836-27.1Av
3 (76mm)"
3 (76mm)"
INTAKE
EXHAUST
COMBUSTION
AIR
MAINTAIN 12 IN. (18 IN. FOR CANADA)
MINIMUM CLEARANCE ABOVE
HIGHEST ANTICIPATED SNOW LEVEL.
MAXIMUM OF 24 IN. ABOVE ROOF.
EXHAUST
ROOF BOOT/
FLASHING (FIELD
SUPPLIED
DRAIN TEE
CONCENTRIC
VENT KIT
(BWH60L46)