Bosch Error Code AU: AU technical settings (service mode) (Tankless)
Bosch error code AU on a tankless water heater means: AU technical settings (service mode). It is also called Bosch diagnostic code AU.
Homeowner? What Bosch code AU means for you
Usually minor Your tankless water heater is reporting: AU technical settings (service mode). This code is usually informational or minor. The safe checks below often clear it; call us if it keeps showing up.
Safe things you can check yourself
- Check that gas reaches the house: other gas appliances work, or the propane tank is not empty.
- Make sure the heater is plugged in and its breaker is on. In winter, keep the power on: it protects the unit from freezing.
- Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
- Check that the hot and cold water valves under the heater are fully open.
- If you have a remote controller, turn it off and on once. If the code comes back, call a technician.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Bosch error code AU mean?
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
Bosch models that use code AU
Greentherm T9800 SE 160Greentherm T9800 SE 199Greentherm T9800 SEC 199Greentherm T9900 i 199Greentherm T9900 SE 160Greentherm T9900 SE 199
Other Bosch Tankless codes
All Bosch Tankless Water Heater error codes →
Bosch code AU: homeowner questions
What does Bosch code AU mean?
AU technical settings (service mode). 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 it safe to keep using my tankless water heater with code AU?
Usually yes. Code AU is normally minor, but if it keeps coming back have it checked.
Can I reset Bosch code AU myself?
You can try one reset (power off for 30 seconds, then on). If Bosch code AU comes back, the cause is still there and a licensed technician should check it.
Who can fix Bosch code AU near me?
Aurora Star Tech Inc. repairs Bosch tankless water heaters in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Tankless Water Heater No Hot Water: What to Check
Troubleshooting guides
- No hot water All brands · Tankless Water Heater
- Water temperature fluctuates All brands · Tankless Water Heater
- Calibrate the water valves (PA water actuator) Bosch · Tankless Water Heater
- Clear an error code with the ON/OFF key Bosch · Tankless Water Heater
- Enter the installer service menu (AU technical settings) Bosch · Tankless Water Heater
- Purge the exhaust circuit (P9 menu) Bosch · Tankless Water Heater
- Read live operation data (OD menu) Bosch · Tankless Water Heater
- Read the last 10 error codes (FH failure history) Bosch · Tankless Water Heater
- Run gas and air auto adjust (UC) Bosch · Tankless Water Heater
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. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.