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To check the draft:
Close all doors and windows to the outside.
Turn on all appliances that force air out of the building.
These include all exhaust/ventilation fans, furnaces, clothes
dryers, wood burning stoves, etc.
Open all doors between the AquaStar and these other
With the control knob set fully clockwise and strong hot
water flow rate, run the unit for at least 10 minutes. The
125B is equipped with a Flue Gas Sensor; it’s mounted on
the right side of the draft diverter (Flue Gas Sensor #20 on
page 17). If the main burners and the pilot flame shut off
during this test it is because the Flue Gas Sensor has
detected inadequate venting. This is a serious health hazard
and must be corrected. Poor venting can result in soot
building up inside the heater, overheating of the heater and
freezing of the heat exchanger in a non-freezing environment
when not in use, which is all a result of negative air flow.
Additional combustion air and/or improved venting is
necessary to correct this.
Note: The burners of an instantaneous “on demand” water
heater such as the AquaStar are only on at the time that
hot water is actually being used, the vent pipe is therefore
cold except for the short durations when hot water is being
used, it is therefore very important that the venting and air
supply be adequate to provide a good positive draft as soon
as the burners turn on.
The AquaStar 125B instantaneous water heaters have built-
in draft diverters and are designed for indoor installation
only. The draft diverter outlet must be connected to an,
unobstructed vent of the same size, or larger.
In Canada, CAN/CGA-B149 Installation Code for detailed
In U.S.A., ANSI Z223.1 - NFPA 54, National Fuel Gas
Code for detailed requirements.
The vent connection for the Aquastar 125B is 5 inches.
However, for installations at high altitude (over 2000 feet
above sea level) a six inch vent is required. A 5” by 6” vent
adaptor must be affixed to the flue collar of the Aquastar
with at least two screws. See Fig. 4.
Fig. 4 - Vent Adaptor for High Altitude Installations
5” X 6” ADAPTOR
USED ON HIGH ALTITUDE
WARNING: Failure TO INCREASE THE VENT SIZE
TO SIX INCHES AND/or assure that the manifold pressure
is set to proper value listed for applications at high altitudes
will cause unsafe venting, asphyxiation, and will void CSA