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MODU-FIRE® FORCED DRAFT
Gas-Fired Boiler Installation
3.12.2 Air Flow Adjustment
There are no required start-up or field adjust-
ments for air flow control. DO NOT attempt to
change any parameters in the blower speed con-
trol (inverter). The Modu-Fire FD uses a micro-
processor controlled variable frequency inverter to
control the speed of the blower. The air flow is set at
the factory. Should an error occur during operation,
the inverter will automatically reset after 30 sec-
onds. If the error recurs, log the flashing error code
and call for authorized service.
3.12.3 Fuel/Air Ratio Adjustment
The fuel/air ratio is controlled by the automatic air
gas ratio valve. This valve is adjusted at the fac-
tory to give 5.5-6% O
2
at high fire and 7.5-7.9%
O
2
at low fire in the exhaust gas. However, the
fuel/air ratio should be checked using a combustion
analyzer at start-up to verify that the combustion is
proper. Remove the vent plug and place the ana-
lyzer probe in the vent as shown. Be sure to replace
the plug after combustion has been set.
Start the boiler. Place the probe of a combustion gas
analyzer in the stack as shown. Using the toggle
switch on the boiler control panel, place the boiler in
High Fire. If the % O
2
is not within the range above,
the gas valve should be adjusted.
To adjust the gas valve on hi fire, turn the top screw
“V” clockwise to reduce the % O
2
or turn it counter-
clockwise to raise the % O
2
. Once high fire is ad-
justed, place the boiler in low fire using the toggle
switch and adjust the % O
2
if necessary, by turning
the bottom screw “N” clockwise to reduce the % O
2
and counterclockwise to increase the % O
2
.
Ratio (V)
Adjust at
Hi Fire
Bias (N)
Adjust at
Low Fire
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