A.O. Smith 100 Series Service Handbook page 38

15. Energize the branch circuit supplying power to the Boiler and turn the Boiler's on/off switch to the on
position. Ensure the Operating Setpoint is set high enough to activate a heating cycle, see Operating
Setpoint Adjustment on page 43. If an external control is using the Boiler's Enable/Disable circuit ensure
the external that control's contacts are closed, see Boiler Controls on page 6. If there is no external control
using the Boiler's Enable/Disable circuit ensure the two wires provided for this circuit are wire nutted
together in the junction box on the back of the Boiler, see Figure 1 on page 6.
Service Note
If the Boiler fails to light off or is experiencing rough starting or rough operation, turn the Boiler's on/off
switch to the off position, see Poor Combustion - Ignition Failure - Rough Start/Operation on page 46 to
determine the cause and correct the problem.
16. Check the dynamic (gas is flowing) supply gas pressure again. Ensure the dynamic supply gas pressure
is within the minimum and maximum supply gas pressure requirements given in the Instruction Manual
that came with the Boiler. Adjust the supply gas pressure at the supply gas regulator as necessary.
17. Allow the Boiler to run for 15 minutes before performing combustion analysis. After 15 minutes of operation
set the Modulate Mode to the Max Mode firing mode, see Modulate Mode Adjustment on page 34.
18. Insert the combustion analyzer sampling probe into the 7/16" hole previously drilled in the Boot Tee.
Follow the manufacturer's instructions for the combustion analyzer being used to sample and record the
CO (carbon monoxide) and CO2 (carbon dioxide) readings.
19. Compare the CO2 readings recorded to the High Fire CO2 parameters in Table 7 on page 36 below. If the
CO2 readings recorded are not within the range given in Table 7 on page 36 adjust as follows:
Remove the round blue plastic cap from the top of the Boiler's 120 VAC Gas Valve. Using a 3mm (7/64")
hex wrench, turn the high fire adjustment screw under the cap counterclockwise to increase or clockwise
to decrease gas flow until the desired CO2 level is reached, see Figure 28 on page 38. Increasing the gas
flow will increase CO2 levels in the vent gases, decreasing gas flow will reduce CO2 levels. Reinstall
blue cap when adjustments are complete. CO readings should be less than 200 ppm (parts per million).
SERVICE NOTE:
Adjust gas flow settings small increments (no more than 1/8 turn) and allow the combustion readings to
stabilize for at least 3 minutes before making further adjustments. If required CO2 levels on start up form
that came with the Boiler differ from levels in this manual adjust to levels shown on start up form.
TABLE 7
HIGH FIRE SETTINGS
Natural Gas
Propane Gas
20. Set the Modulate Mode to the Min Mode firing mode, see Modulate Mode Adjustment on page 34. Allow the
Boiler to run for 5 minutes and then record the CO2 and CO levels.
21. Compare the CO2 readings recorded to the Low Fire CO2 parameters in Table 8 below. If the CO2
readings recorded are not within the range given in Table 8 adjust as follows:
Remove the small metal slotted cap near the outlet of the Boiler's 24 VAC gas valve. Using a TORX®
T40 or a 5mm hex wrench turn the low fire adjustment screw under the cap clockwise to increase or
counterclockwise to decrease gas flow until the desired CO2 level is reached, see Figure 28 on page 38.
Increasing the gas flow will increase CO2 levels in the vent gases, decreasing gas flow will reduce CO2
levels. Reinstall the slotted cap when adjustments are complete. CO readings should be less than 200
ppm.
TABLE 8
LOW FIRE SETTINGS
Natural Gas
Propane Gas
22. Set the Modulate Mode to the Max Mode firing mode again and recheck CO2 readings, fine tune the gas
flow as necessary.
36
8.5 - 11.0 % CO2 (CO < 200 ppm)
9.5 - 12.0 % CO2 (CO < 200 ppm)
7.5 - 9.5 % CO2 (CO < 200 ppm)
9.5 - 12.0 % CO2 (CO < 200 ppm)
Servicing should only be performed by a Qualified Service Agent