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6 720 607 026

VENTING

Vent pipe connection.

WARNING: Do not reduce the vent pipe size. See Fig. 4

for high altitude installations

The heater must be vented to the outside following all local
ordinances and specifications for installing a gas appliance
vent  or  chimney.  The  heater  must  be  located  as  close  as
practicable to a vertically rising chimney or vent that has a
listed vent cap at its termination point. The venting system
must be designed and constructed so as to develop a posi-
tive flow adequate to remove flue gasses to the outdoors.

Consult the National Fuel Gas Code if the vent will have
elbows  or  share  venting  with  another  natural  draft

Roof pitch

H (minimum) feet

meters

Flat to 6/12

1.0

0.30

6/12 to 7/12

1.25

0.38

Over 7/12 to 8/12

1.5

0.46

Over 8/12 to 9/12

2.0

0.61

Over 9/12 to 10/12

2.5

0.76

Over 10/12 to 11/12

3.25

0.99

Over 11/12 to 12/12

4.0

1.22

Over 12/12 to 14/12

5.0

1.52

Over 14/12 to 16/12

6.0

1.83

Over 16/12 to 18/12

7.0

2.13

Over 18/12 to 20/12

7.5

2.27

Over 20/12 to 21/12

8.0

2.44

GAS VENT TERMINATIONS FOR LISTED VENT CAPS

Listed  vent  cap

Lowest  discharge
opening

H  (minimum)  height
from  roof  to  lowest
discharge  opening

Roof  Pitch

IS X/12

12

X

Listed  gas  vent

Figure A

Figure B

Establish  a  one  foot

rise  before  any  elbows

M

IN

IM

U



F

E

ET 

(1

.8M

)

Listed  vent  cap

plasterboard, can cause failure of mounting.
In earthquake-prone zones, CEC recommends that installers
use a large washer and lag screw through the existing holes
used to hang the heater to affix the upper third of the heater
to the mounting board. To affix the lower third of the heater,
CEC  recommends  that  two  new  holes  be  drilled  in  the
heater’s frame, each one 16 inches below the top two holes,
and  that  washers  and  lag  screws  be  used  to  secure  the
lower portion of the heater to a spacing board.

Before installing the unit, be certain you have the correct
heater  for  your  type  of  Gas  –  Propane  or  Natural  Gas.
Identification labels

 

are found on the shipping box, and on

the rating plate which is located on the right side panel of

the cover. Also, each burner orifice is stamped with a number
(79 for LPG and 120 for Natural Gas).

Fig. 2 - Mounting the Heater

WALL  STUDS

1” X 4”

SPACE BOARD

SUPPORT
BOARD

13 ¼”

Fig. 3 - Incandescent Particle Tray Illustration

The incandescent particle tray (shipped loose in the carton
with the water heater) must be attached at  the bottom of
the water heater front cover at the time of installation. Use
the screws provided. See figure 3

SCREWS

INCANDESCENT  PARTICLE  TRAY

appliance. The heater should never be common vented
with a mechanically vented appliance.  Single wall vent
pipe is not recommended, if used consult the National
Fuel Gas Code.

Horizontally  venting  to  a  sidewall  vent  terminator  or  a
vertically constructed vent stack along an outside wall of a
building is not permissible. A Powervent (Model AQ-1), with
a  proof-of-draft  safety  interlock  device,  is  required  and  is
available in order to sidewall vent. Contact your dealer.  

In

the  Commonwealth  of  Massachusetts:  Powervented
applications must utilize proof-of-draft safety interlock
device.

VERTICAL GAS VENT:

 A 5 inch diameter gas vent constructed

of double wall Type B gas vent is recommended. 6 inch is
required  in  elevations  greater  than  2000  feet,  see  Fig.  4.
Any gas vent section that is greater than 45 degrees from
the vertical is considered horizontal. Horizontal sections must
slope upwards at least ¼ inch for every foot of its horizontal
length and be properly supported.  Keep the horizontal section
short and avoid too many elbows. The minimum vertical gas
vent  height  allowed  is  6  feet;  horizontal  vent  connectors
and elbows are not to be considered in the total gas vent
height. All gas vent sections must be secured to each other
with sheet metal screws and be properly supported.

The gas vent constructed of double wall Type B gas vent
must  terminate  above  the  roof  surface  with  a  listed  vent
cap at a height that’s in accordance with Figure A or B and
their table, provided they are at least 8 feet (2.4 m) from a
vertical wall or similar obstruction. All other gas vents that
are not able to terminate within the minimum specified height
allowed must terminate not less than 2 feet (0.6 m) above
the highest point where it’s passed through the roof and at
least 2 feet (0.6 m) higher than any vertical wall or similar
obstruction within 10 feet (3.1 m).

Summary of Contents for GWH 425 HN

Page 1: ...aintenance 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 ...

Page 2: ...er appliance WHAT TO DO IF YOU SMELL GAS Do not try to light any appliance Do not touch any electrical switch do not use any phone in your building Immediately call your gas supplier from a neighbor s phone Follow the gas supplier s instructions If you cannot reach your gas supplier call the fire department Installation and service must be performed by a qualified installer service agency or the g...

Page 3: ... will not exceed the heating capacity of the heater On Off Switch to activate system Red LED indicator flashes with low water pressure Green LED indicator main burner operation BOSCH is constantly improving our products therefore specifications are subject to change without prior notice 425 HN LP and 425 HN NG Specifications Gas Input max 117 000 Btu hr min 28 000 Btu hr Water Connection Thread fi...

Page 4: ...INIMUM INSTALLATION CLEARANCES FROM COMBUSTIBLE AND NON COMBUSTIBLE MATERIALS FOR ALCOVE OR CLOSET INSTALLATIONS FRONT VIEW SIDE VIEW MODEL 425HN MODEL 425 HN TOP A 12 FRONT B 4 BACK 0 SIDES 4 FLOOR C 12 VENT DIAMETER 5 ...

Page 5: ...control which has been underwater PROPER LOCATION FOR INSTALLING YOUR HEATER Carefully select the location of your new heater For your safety and for proper heater operation you must provide an abundant supply of combustion air and a proper venting Fig 1 Water heater drain plug The heater may still operate even when improperly vented It will however be less efficient and could eventually damage th...

Page 6: ...00 Btu hr if all air is taken from the outside by horizontal ducts 4000 Btu hr if all air is taken from the outside by direct openings or vertical ducts Or the confined space must be provided with one permanent opening or duct that is within 12 inches of the ceiling of the enclosure This opening must have a minimum free area of one square inch per 3000 Btu hr if all air is taken from the outside b...

Page 7: ...s stamped with a number 79 for LPG and 120 for Natural Gas Fig 2 Mounting the Heater WALL STUDS 1 X 4 SPACE BOARD SUPPORT BOARD 13 Fig 3 Incandescent Particle Tray Illustration The incandescent particle tray shipped loose in the carton with the water heater must be attached at the bottom of the water heater front cover at the time of installation Use the screws provided See figure 3 SCREWS INCANDE...

Page 8: ...ter heater to a masonry chimney the following connector guidelines must be followed for safe and proper operation An approved gas vent connector must be attached to the top of the water heater and rise vertically at least 12 before entering into an approved gas vent connector elbow Any gas vent section that is greater than 45 degrees from the vertical is considered horizontal If a horizontal vent ...

Page 9: ...the gas lines or malfunction of the supply system the gas valve and regulator must be checked for safe operation Make sure that the regulator vent is protected against blockage When your connections are made check for gas leaks at all joints not just the ones you made Apply some soapy water to all gas fittings and gas valve Soap bubbles are a sign of a leak NOTE Do not apply soap solution to the p...

Page 10: ...l length of piping and then adding 5 ft for every elbow or T to the actual length Use the charts below to determine the pipe diameter necessary to accommodate the BTU demand of the unit If there are more gas drawing appliances on the line size according to the maximum amount of BTU demand Follow boxed numbers for piping just one 425 HN example 3 4 B I Natural Gas pipe for 30 ft will handle 152 000...

Page 11: ...runs as short as possible When facing the heater the cold water inlet will be on the right and the hot water outlet on the left Although water piping throughout the building may be other than copper copper or galvanized piping should be used when connecting to the heaters male NPT flex connectors follow local codes if more stringent Plastics or other PEX type plumbing line materials are not suitab...

Page 12: ...icator light is flashing this is a warning that the water pressure is not enough to ignite the main burner 6 Turn the hot water faucet on to the minimum flow rate required to activate the heater The automatic ignition system first ignites the safety pilot burner which then ignites the main burner in about 4 seconds 7 The green LED indicator is on when the main burner is on 8 The pilot flame will e...

Page 13: ...ers have yellow flames while others have good flames it is likely that dust lint or spider webs have partially clogged the burner venturis To clean the burners contact a gas service person Mineral Scale Build up The 425 HN heater when operated at lower temperature settings does not accumulate mineral build up If however the heater is used at the higher temperature settings and the water has a high...

Page 14: ...and component parts must be totally free of dirt In hard water areas mineral deposits can eventually 3 5 years in hard water areas corrode the water valve parts to a point where they will need replacing Any sign of moisture or corrosion at the joint of the water valve and the gas valve is a sign that the water valve components need to be serviced immediately 7 Poor circuit connections at the ECO o...

Page 15: ...is mixing with the hot water between the 425 HN and the outlet Compare water temperature at outlet of the 425 HN hold the 425 HN outlet pipe with your hand and at the tap If these two are very different check for mixing valve or plumbing crossover see NO SPARK AT THE PILOT paragraph 4 5 Parts in water valve are dirty or damaged which will prevent the gas valve from being fully opened Water valve m...

Page 16: ... 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 manufactures 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 adjusted to produce a more comfortable hot water temperature S...

Page 17: ...ner manifold gas pressure test nipple 4 Main gas burner 5 Pilot gas tubing 6 LED failure indicator 7 on off switch 8 LED operation indicator 9 Water valve 10 Temperature adjustment selector 11 Gas inlet gas pressure test nipple 12 Hose 3 1 4 10 11 2 9 8 6 7 5 12 6 720 606 804 10 1AL ...

Page 18: ...18 6 720 607 026 Fig 15 INTERIOR COMPONENTS DIAGRAM AND PARTS LIST ...

Page 19: ...7 Pilot electrovalve 8 708 501 249 18 Burner electrovalve 8 708 501 250 19 O ring 8 700 205 023 20 Hydro generator 8 707 406 043 21 Cold water pipe 8 700 705 947 22 Outlet flex hose 8 700 703 139 23 Washer 8 700 103 658 24 Water valve 8 707 002 649 25 Water valve cover 8 705 500 101 26 Diaphragm 8 700 503 053 27 Water inlet filter 8 700 507 001 28 Water valve selector screw 8 708 500 289 29 Volume...

Page 20: ...20 6 720 607 026 Fig 16 Flow chart of 425 HN ...

Page 21: ... may not apply to you This warranty gives specific legal rights You may also have other rights which vary from state to state Fifteen Year Limited Warranty General BOSCH PRO water heaters are warranted by the Manufacturer BOSCH through Controlled Energy Corp Controlled Energy Corp CEC will furnish a replacement heat exchanger and will furnish a replacement of any other part which fails in normal u...

Page 22: ...22 6 720 607 026 ...

Page 23: ...23 6 720 607 026 ...

Page 24: ...k Waitsfield Vermont 05673 Phone 866 330 2730 Fax 802 496 6924 www protankless com techsupport protankless com 3 1 e g a p e e s E L B A T E C N A N E T N I A M R A E Y Y R E V E S R A E Y 2 Y R E V E S R A E Y 5 3 Y R E V E E V L A V R E T A W E T A C I R B U L E V L A V R E T A W D L I U B E R N E E R C S R E T L I F R E T A W T C E P S N I Y L B M E S S A T O L I P T C E P S N I Y L B M E S S A...

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