Commissioning A Bosch Greenstar Boiler

When you are commissioning a Bosch Greenstar Wall Boiler, it’s important to follow these general steps.

Note: Use the commissioning log found on page 79 of the Installation and Service Instructions to follow along. The tools needed for commissioning include a Combustion Analyzer, a Gas Manometer, a 4mm Allen wrench, and a small and large flathead screw driver.

  • Verify proper piping and wiring to the Boiler.
    • Boiler LWCO wired to terminals 8 and 9 on orange plug, with a separate transformer for power (boiler does not have 24 volts on board).
    • Power and pump connections on the bottom of the boiler are correct.
    • Low loss header sensor is plugged to connector.
    • Either Bosch controls system is used on BB terminals on gray plug or a standard thermostat connection is made on terminals 2 & 4 on the gray plug.
    • If an indirect tank is used, use the indirect thermistor supplied with the boiler. Check that the plug is properly secured to board.
    • Make sure the air eliminator, expansion tank, low loss header, and boiler make up water are properly piped.

  • Verify vent and combustion piping material, diameter, and length are in accordance with the installation manual.
  • Adjust the temperature dials to desired set points for both Central Heating and DHW (if used).

  • Check incoming gas type and pressure to the Boiler
    • Reading can be made by checking pressure at the port shown to the right.

  • Set the Gas-Air Ratio (CO2 and/or O2 levels)
    • Remove flue gas test port plug on flue adaptor, and insert Combustion Analyzer.
    • To put the boiler into test mode press the  button until the display shows . Briefly press the  button, the display should show  signaling that the boiler is now in high fire.
    • Remove the grey cap covering the throttle screw and adjust the Air Mix Throttle screw (using a Slotted screw driver) shown below as required to achieve CO2 of 9.4% for natural gas or 11.0% for Propane. Allow enough time for sample to travel through the test hose to reach the tester.

  • Press the  button once, boiler display should show  signaling the boiler is now in low fire. Remove adjustment screw cap from gas valve using a 4mm allen wrench. Make adjustment on the adjustment screw shown below until CO2 is 8.6% for natural gas or 10.4% for propane.


  • Once low fire adjustments are complete, put the boiler back into high fire by pressing the  button until the boiler control is showing . Verify maximum CO2 reading once again.
  • Record the CO2, O2, and CO (should be under 200ppm) levels at minimum and maximum output on the commissioning log. Reinstall flue test port plug, gas valve screw cover and air throttle cover. Repeatedly press the  button until the light goes out. The display will go back to showing the supply temperature.

Refer to this chart for proper CO2 and O2 levels. Remember CO should always be below 200ppm.

Note: CO2 gives a more accurate setting than an O2 setting, so if you have a tester for both, use the CO2.

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