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Bosch · Tankless water heater

AU AU technical settings (service mode)

Menu / mode display Bosch Greentherm T9800 SEBosch Greentherm T9900 SE

What the display is showing

Installer-only service menu. It opens a password prompt and then lists technical items such as gas type, temperature limit, combustion adjust, water actuator, bypass valve, appliance type, region and demonstration. The installer password is printed in the installation manual (section 6.6).

Applies to: Greentherm T9800 SE 160/199 and T9900 SE 160/199 tankless water heaters

What to do

  1. Open Information / Adjustments, touch until AU Technical Settings shows
  2. Touch the symbol and enter the password
  3. Touch the up or down symbols to move between menus

Models that show this code

6 models in Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

Greentherm T9800 SE 160Greentherm T9800 SE 199Greentherm T9800 SEC 199Greentherm T9900 SE 160Greentherm T9900 SE 199Greentherm T9900 i 199

Other codes on the same units

  • P9 P9 purge menu
  • AA Flue gas temperature too high, power limited
  • AC AC consumption
  • AD Power derate warning
  • BB Fan calibration after missed ignitions
  • BC Repeated fan calibration with similar values
  • Burner symbol Burner status symbol - burner on
  • CA Water flow above 9.2 gpm

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Source: Bosch Greentherm T9800 SE 160-199 installation 6720816815 (06.2023), 6.6 Service menu - AU Technical Settings p.52; T9900 SE 160-199 installation 6 720 813 635 (2024-06) same section. Summarized in our own words; check the original manual for your model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.