Thermo Pride Gas/Propane Furnace Induced Draft Highboy/Counterflow/Horizontal MHA1 - Manual (Page 37)

All installations and services must be performed by qualified service personnel.
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b. Turn on the fuel gas and cause the appliance to activate the heating
section by answering a “call for heat”.
c. Allow the heating section to operate for 15 minutes.
d. Note the manifold gas pressure.
e. To adjust the pressure, remove the brass screw from the regulator on the
outlet side of the gas control valve. Using a common screwdriver, increase
the manifold pressure by turning the screw inward (clockwise), or
decrease it by turning the screw outward (counterclockwise).
Adjustments to the listed pressure must not exceed 0.3 in. W.G. A
0.3 in. W.G. adjustment will change the input approximately 4.0%.
f. Measure the heat input rate by counting the number of seconds required
for the appliance to consume a specified quantity of gas. Refer to the
preceding procedure to calculate the heat-input rate.
g. If required, repeat the manifold pressure adjustment again. Repeat the
input rate measurement.
h. When the input rate adjustment has been completed, shut off the fuel gas
to the appliance. Remove the pressure gage. Reinstall the manifold pipe
plug using a thread compound resistant to the action of LP gases.
Replace the regulator screw (cap) in the gas valve.
If an input rate within the allowable range cannot be obtained with the present
orifice over the range of manifold pressures given, make sure the gas supply
pressure is within the specified range. If the supply pressure is less than
required, the upstream supply pressure regulator may have to be adjusted to
increase the pressure. If increasing the gas supply pressure fails to provide
adequate gas pressure at the unit, the supply piping may have to be modified to
reduce pressure drop.
C. Burner Adjustment
There are no manual adjustments to the main burners. With the burner
compartment door removed, the flames can be observed. Natural gas flames
should be relatively short in length, have well defined shapes, and are bright light
to deep blue in color, refer to Figure 10.
NOTICE: For appliance operation with propane gas, it is not unusual to
observe mostly blue flames having yellow or yellow-orange tips.