Bosch GWH 260 PN Service Bulletin Booklet page 5

NEGATIVE AIR & FREEZE
PREVENTION
MODELS: 1000P, 1600P, 1600H,
260PN, 425PN, 425HN
Negative Air
• Negative air pressure in a str ucture occurs when air con-
sumed by fuel burning appliances or exhaus t systems in that
structure exceeds the amount of air available.
• Here is a list of items tha t consume air within a typical house-
hold:
• Stove exhaust fans
• Furnaces
• Water heaters
• Fireplaces/ Woodstoves
• Bath fans
• Dryers
• All of these items must be taken into account when making
provisions for a proper amount of fresh air from the outside.
• If the building is new cons truction, air infiltration from the
outside will be limited and provisions for extra air supply
should be made. If the building is older construction, air may
infiltr ate into the house through unplanned sources such as
window fr ames, door jams, sill plates or idle chimney flues.
These sour ces still may not be providing the adequate amount
of air and additional sources of fresh air should be consid-
ered.
Why Negative Air is Bad
Cold air from the outside is dr awn through the water heater's
flue pipe because other fuel burning appliances or exhaust
systems in the str ucture require more air than the dwelling
can supply. When the required amount of air for the fuel
burning appliances or exhaust systems in t he structure is
not being supplied to them, they find the flue pipe on the
water heater an acceptable means of supplying themselves.
Thus, freezing cold air is pulled down the water he ater's flue,
drawn o ver t he copper heat exchanger, potentially freezing
it and the water valve below. Because, when idle, the water
heater holds only cold w ater, fr eezing can happen quickly
possibly causing leaks or r uptures in the heat exchanger and/
or the water valve. The water he ater does not pull air through
its flue pipe – if you w ere to remove the heater, the air would
continue to come down your f lue pipe. You must ha ve the air
balanced in the s tructure to correct this pr oblem. Consulta-
tion with a heating, ventilating and air conditioning (HVAC)
specialist is recommended.
Note: Poor venting can result in excessive
sooting around the water heater, overheat-
ing, and release dangerous carbon mon-
oxide into the living space causing seri-
ous injury and/or death.
Note: Damage to the heater as a result of
improper venting will not be covered un-
der warranty.
©BBT NORTH AMERICA CORPORATION
Bosch Group
W W W W W ARNIN ARNIN ARNIN ARNING G G G G
ARNIN
LP & N LP & N G ARE EXTREMEL G ARE EXTREMEL
LP & N LP & NG ARE EXTREMEL LP & N G ARE EXTREMELY FL G ARE EXTREMEL
T T T T T AKE EXTRA PRECA AKE EXTRA PRECA AKE EXTRA PRECA AKE EXTRA PRECAUTIONS WHEN
AKE EXTRA PRECA
PERFORMIN PERF PERF ORMIN ORMIN G ANY W ORMIN G ANY W G ANY W G ANY WORK T
PERF PERF ORMIN G ANY W
Checking for Negative Air
1. Close all doors and windows in the building.
2. Operate all fuel bur ning appliances and exhaus t systems in
the building at full capacity with the exception of the tankless
water heater. Allow time for t hese items to utilize the air in
the str ucture. Up to one hour may be necessary.
3. Remove the cover from the tankless unit and hold a r ecently
extinguished ma tch, candle, or any other visible smoke source
in front of the triangular opening on the draft diverter.
4. The smoke should be sucked quickly into the opening and up
the exhaust vent. If the smok e is blown back, a negative air
situation exists and must be corrected. See the combustion
air section in the manual for specifications.
5. Now run the he ater for 10 minutes, then hold a smoke source
at the top right side of the draf t diverter. The smoke should
be drawn in the louvers on the side. If this is not the ca se,
the unit is not drafting properly and flue gases are being
exhausted into the space in which the heater is ins talled.
This is not safe and must be corrected. Reference the vent-
ing section in the manual to ensure venting is in accordance
with the manufacturer's specif ications.
S tep 3: Hold extiguished
matc h here
DRAFT DIVERTER FOR:
1000P, 1600P, 1600H,
260PN, 425PN, 425HN
340 Mad River Park, Waitsfield, VT 05673
Y FL Y FL AMMABLE SO AMMABLE SO
Y FLAMMABLE SO Y FL AMMABLE SO AMMABLE SO
UTIONS WHEN UTIONS WHEN UTIONS WHEN
UTIONS WHEN
ORK T ORK T ORK TO THE HEA O THE HEATER O THE HEA O THE HEA TER TER TER
ORK T O THE HEA TER
S tep 5: Hold extiguished
matc h here
Bosch Water Heating
CT-05
page 1 of 1
rev 10/06