AO Smith BTR120 Manuel D'instructions page 30

Should it be necessary to adjust the gas pressure to the burners
to obtain the full input rate, the steps below should be followed:
3. Remove the regulator adjustment sealing cap and adjust the pressure
by turning the adjusting screw with a screwdriver. See Figure 24.
Clockwise to increase gas pressure and input rate.
Counterclockwise to decrease gas pressure and input rate.
4. "Clock" the meter as in step 2 above.
5. Repeat steps 3 and 4 until the specified input rate is achieved.
6. Turn the gas control knob to PILOT. Remove the pressure
gauge and replace the sealing cap and the Allen wrench set
screw in the pressure tap opening.
UNDER NO CIRCUMSTANCES SHOULD THE GAS INPUT EXCEED
THE INPUT SHOWN ON THE HEATER MODEL AND RATING
PLATE. OVERFIRING COULD RESULT IN DAMAGE OR SOOTING
OF THE HEATER.
30
FIGURE 24.