HVACopediaBosch · Tankless water heater
UC UC auto adjust (gas and air)
What the display is showing
Automatic gas and air adjustment inside the combustion adjust menu. It takes about 15 minutes and needs only enough hot water flow. A green check mark shows when it finishes. MA manual adjust is the alternative. Needed after an LPG conversion, repeated unresolved errors, or replacing the control unit, fan or gas valve.
Applies to: Greentherm T9800 SE 160/199 and T9900 SE 160/199 tankless water heaters
What to do
- Enter AU Technical Settings and open the combustion adjust menu
- Select UC Auto Adjust
- Open hot water taps when Open Taps shows
- Wait for the green check mark
Models that show this code
6 models in Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE
Other codes on the same units
- HS HS about
- OD OD operation data
- Open Taps Open Taps message during auto adjust
- PA PA water actuator (valve calibration)
- PE PE appliance type (read-only data)
- SA SA settings menu
- Setpoint display Set temperature shown on touch display
- Solar mode Solar mode indicator
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Source: Bosch Greentherm T9800 SE 160-199 installation 6720816815 (06.2023), 8.11 Gas and Air Adjustment pp.60-61; 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.