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Bosch · technician tips

Bosch service menus, test modes and resets

25 tips for boiler, heat pump, tankless water heater: access codes, button combinations, test modes and the resets you need at the appliance.

Jump to: Access & passwords (2) · Button combinations (1) · Service & test modes (15) · Reset & cancel (4) · Commissioning (3)

Access & passwords

Installer and service menu codes, and how to get into them.

Open the service functions (Greenstar service button)

Boiler · Bosch Greenstar

Holding the service button until it lights opens the service functions; the display shows a function number such as 1.A. Second-level functions (8.A onward) need ECO + key pad lock together. Service mode times out after 15 minutes without a button press.

  1. Keep the service button pressed until it lights
  2. Scroll with the key pad lock button (down) or ECO button (up)
  3. Tap the emissions test button to see a value; change it with the same two buttons
  4. Hold the emissions test button to save, or press it briefly to leave without saving
  5. Second level: with the service button lit, press ECO and key pad lock together until 8.A shows

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.1 Guideline to service functions p.57-58. Written in our own words; check the manual for your exact model.

Enter the installer service menu (AU technical settings)

Tankless water heater · Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

Installer-only service menu behind a password prompt; the password is printed in the installation manual (section 6.6).

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

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

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; check the manual for your exact model.

Button combinations

Key presses that open menus, show readouts or switch modes.

Lock or unlock the key pad

Boiler · Bosch Greenstar

The key pad lock blocks the high limit dial, the DHW thermostat and every button except ON/OFF, emissions test and reset. A lock symbol alternates with supply temperature when on.

  1. Keep pressing the key pad lock button until the lock symbol alternates with the supply temperature
  2. To unlock, keep pressing the same button until only the supply temperature shows

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 8.14 Activating the key pad lock p.57. Written in our own words; check the manual for your exact model.

Service & test modes

Forced fan, low and high fire, test and diagnostic modes, error history and live data.

Force minimum or maximum output for 15 minutes (function 2.F)

Boiler · Bosch Greenstar

Temporary test mode: 00 normal, 01 minimum output for 15 minutes, 02 maximum output for 15 minutes. The boiler returns to normal after 15 minutes or when aborted.

  1. Open service functions with the service button and scroll with key pad lock / ECO
  2. Select 2.F, choose 01 or 02, save

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Lock the boiler at minimum or maximum output (function 9.A)

Boiler · Bosch Greenstar

Values: 00 normal, 01 permanently minimum output, 02 permanently maximum output. The display shows 9.A while active.

  1. Reach the second level (service button, then ECO and key pad lock together) and scroll to 9.A
  2. Choose 01 or 02, and set 00 to return to normal

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Move the 3-way valve to centre to drain (function 7.b)

Boiler · Bosch Greenstar

After value 01 is saved the 3-way valve moves to its centre position so the system can be drained and the motor removed. Leaving the function resets it to 00.

  1. Open service functions with the service button and scroll with key pad lock / ECO
  2. Select 7.b, set 01 and save

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Read the latest stored fault code (function 6.A)

Boiler · Bosch Greenstar

Shows the most recent fault code stored in the boiler. Read-only.

  1. Open service functions with the service button and scroll with key pad lock / ECO
  2. Select 6.A to read the code

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Start or stop the building drying program (function 7.E)

Boiler · Bosch Greenstar

Starts and stops the slab drying program. While it is on, the gas settings cannot be adjusted.

  1. Open service functions with the service button and scroll with key pad lock / ECO
  2. Select 7.E to start or stop it

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Start the air-purge routine (function 2.C)

Boiler · Bosch Greenstar

Starts the air purge by hand, for example after servicing. Values: 00 off, 01 purge once then back to 00, 02 permanently on.

  1. Open service functions with the service button and scroll with key pad lock / ECO
  2. Select 2.C and press the emissions test button
  3. Choose 01 and save by holding the emissions test button

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Start the emissions test (chimney sweep) mode

Boiler · Bosch Greenstar

Holding the emissions test button starts boiler test mode for gas pressure and combustion checks; a brief tap toggles between maximum set heating output and maximum nominal output.

  1. Keep the emissions test button pressed until it lights
  2. Tap it to switch between max set heating output and max nominal output
  3. Keep it pressed until the light goes out to return to the supply temperature

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 8.3 Dynamic gas pressure test p.50. Written in our own words; check the manual for your exact model.

Test ignition with continuous sparking (function 8.F)

Boiler · Bosch Greenstar

Gives continuous sparking without gas to test the ignition parts. Never leave it on for more than 2 minutes at a time because it can damage the ignition transformer.

  1. Reach the second level (service button, then ECO and key pad lock together) and scroll to 8.F
  2. Set 01, test, then set 00

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Force cooling for charging with the FORCE button

Heat pump · Bosch IDS 2.0, Bosch IDS Light, Bosch IDS Premium Connected

A short press of FORCE (SW1) while the unit runs in cooling puts it in forced full-capacity operation for checking charge. On IDS 2.0 the display then shows a bar symbol followed by the compressor frequency.

  1. Start the system in cooling mode
  2. Short press the FORCE button on the outdoor board
  3. Allow about 10 minutes to ramp up and 20 minutes to stabilise before taking charging readings

Applies to: BOVA IDS 2.0, IDS Premium Connected and IDS Light heat pumps

Source: Bosch IDS Premium Connected BTC 762003301 D (02.2025), 17.2 Subcooling Charging p.43-44; IDS 2.0 service Rev3 (07.2021), 10.2.2 Force Mode Operation p.32. Written in our own words; check the manual for your exact model.

Read system values with the CHECK button (point check)

Heat pump · Bosch IDS Light, Bosch IDS Premium Connected

Pressing CHECK on the outdoor board steps through system values: each press shows the point number then its value after 1 second. After 20 seconds on a point the display returns to normal. Examples: 0 unit capacity, 1 mode (0 standby, 2 cooling, 3 heating), 2 set compressor speed in Hz, 3 last fault code.

  1. Press the CHECK button (SW2) on the control board
  2. The point number shows, then its value after 1 second
  3. Press CHECK again for the next point
  4. Do nothing for 20 seconds to return to the normal display

Applies to: BOVA IDS Premium Connected (36-60) and IDS Light (BOVA15) heat pumps

Source: Bosch IDS Premium Connected BTC 762003301 D (02.2025), 18.9 System Protection Status Codes p.49 and 18.10 Parameter Point Check Table p.50; IDS Light BTC 762003308 D (01.2025), 17.9 p.43 and 17.10 p.44. Written in our own words; check the manual for your exact model.

Run the gateway diagnostic (Factory + Connect buttons)

Heat pump · Bosch IDS Premium Connected

Holding the Factory button for 3 to 5 seconds puts the gateway in diagnostic mode; Connect then runs a full diagnostic. A fault shows as a red Fault LED blink code.

  1. Hold the Factory button for 3 to 5 seconds
  2. Press the Connect button to run the full diagnostic
  3. Read the Fault LED blink count

Applies to: IDS Premium Connected gateway

Source: Bosch IDS Premium Connected BTC 762003301 D (02.2025), Gateway light indications table (troubleshooting section) and 20 Gateway Functionality p.69. Written in our own words; check the manual for your exact model.

Start a manual defrost test (hold FORCE 6 s)

Heat pump · Bosch IDS 2.0, Bosch IDS Light, Bosch IDS Premium Connected

Holding FORCE for 6 seconds starts a forced defrost test. The unit must be in a heating call and have run 8 minutes or more. Defrost starts after about 40 seconds and the display shows dF.

  1. Make sure there is a heat call and the unit has run 8 minutes or more
  2. Press and hold the FORCE button for 6 seconds
  3. Wait about 40 seconds; the display shows dF
  4. For a second test wait 5 minutes and repeat

Applies to: BOVA IDS 2.0, IDS Premium Connected and IDS Light heat pumps

Source: Bosch IDS Premium Connected BTC 762003301 D (02.2025), 18.4 Defrost Description p.46; IDS Light BTC 762003308 D, Manual Defrost; IDS 2.0 service Rev3, 10.2.1 p.31. Written in our own words; check the manual for your exact model.

Purge the exhaust circuit (P9 menu)

Tankless water heater · Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

About 2 seconds after entering the menu the fan starts and keeps running until the menu is left.

  1. Open Information / Adjustments, touch until P9 Purge shows
  2. Touch the symbol to start; the fan starts after about 2 seconds
  3. Exit the menu to stop the fan

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

Source: Bosch Greentherm T9800 SE 160-199 installation 6720816815 (06.2023), 6.5.4 P9 Purge p.52; T9900 SE 160-199 installation 6 720 813 635 (2024-06) same section. Written in our own words; check the manual for your exact model.

Read live operation data (OD menu)

Tankless water heater · Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

OD shows live readings for troubleshooting: heat exchanger outlet/inlet/outlet NTCs, air pressure, fan speed, water flow, ambient and exhaust NTCs, external tank temperature, barometric pressure and ionization value.

  1. Open P4 Information and select OD Operation Data
  2. Touch the symbols to scroll through the readings

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

Source: Bosch Greentherm T9800 SE 160-199 installation 6720816815 (06.2023), 6.5 Information / Adjustments menu pp.47-48; T9900 SE 160-199 installation 6 720 813 635 (2024-06) same section. Written in our own words; check the manual for your exact model.

Read the last 10 error codes (FH failure history)

Tankless water heater · Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

FH shows the last 10 error codes; three dots mean no error has occurred. The date symbol shows when an error happened.

  1. Open P4 Information, select FH Failure History
  2. Touch up or down to move between stored errors
  3. Touch the date symbol to see the date and hour of an error

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

Source: Bosch Greentherm T9800 SE 160-199 installation 6720816815 (06.2023), 6.5 Information / Adjustments menu pp.47-48; T9900 SE 160-199 installation 6 720 813 635 (2024-06) same section. Written in our own words; check the manual for your exact model.

Reset & cancel

Clearing lockouts, service reminders and fault history; skipping purge or de-air programs.

Reset the service-due indication (function 5.A)

Boiler · Bosch Greenstar

Clears the service due indication that alternates on the display after the inspection interval.

  1. Open service functions with the service button and scroll with key pad lock / ECO
  2. Select 5.A and confirm to reset the indication

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Restore factory settings (function 8.E)

Boiler · Bosch Greenstar

Resets all boiler parameters, including all service functions, to factory settings. Re-enter the values from the commissioning report afterwards.

  1. Press the service button until it lights, then ECO and key pad lock together for the second level
  2. Scroll to 8.E and press the emissions test button; the display shows 00
  3. Hold the emissions test button until the confirmation appears

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Written in our own words; check the manual for your exact model.

Restart the gateway (Reset button)

Heat pump · Bosch IDS Premium Connected

The Reset button powers the gateway off and back on.

  1. Press the Reset button once

Applies to: IDS Premium Connected gateway

Source: Bosch IDS Premium Connected BTC 762003301 D (02.2025), Gateway light indications table (troubleshooting section) and 20 Gateway Functionality p.69. Written in our own words; check the manual for your exact model.

Clear an error code with the ON/OFF key

Tankless water heater · Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

Holding ON/OFF for over 3 seconds clears an error code from the display; the appliance then runs its start-up sequence. If the error returns, call a licensed professional.

  1. Touch and hold the ON/OFF key for more than 3 seconds
  2. Wait for the start-up sequence

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

Source: Bosch Greentherm T9800 SE 160-199 installation 6720816815 (06.2023), 6.3 Error code reset p.45; T9900 SE 160-199 installation 6 720 813 635 (2024-06) same section. Written in our own words; check the manual for your exact model.

Commissioning

Start-up and set-up steps that are easy to miss.

Pair the gateway by Bluetooth (Connect button)

Heat pump · Bosch IDS Premium Connected

Holding Connect for at least 4 seconds turns Bluetooth on so the app can pair with the gateway.

  1. Hold the Connect button for at least 4 seconds
  2. Watch the blue LED: 1 blink means pairing mode

Applies to: IDS Premium Connected gateway

Source: Bosch IDS Premium Connected BTC 762003301 D (02.2025), Gateway light indications table (troubleshooting section) and 20 Gateway Functionality p.69. Written in our own words; check the manual for your exact model.

Calibrate the water valves (PA water actuator)

Tankless water heater · Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

Needed after replacing the main or bypass valve or the electronic control unit; takes several minutes and needs hot water flowing (bypass calibration needs 0.80 to 1.80 gpm).

  1. Enter AU Technical Settings, then open PA
  2. Select MF main valve or BP bypass valve and touch OK
  3. Open a hot water tap and do not interfere until completion shows

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

Source: Bosch Greentherm T9800 SE 160-199 installation 6720816815 (06.2023), 6.7 Water valves calibration p.53; T9900 SE 160-199 installation 6 720 813 635 (2024-06) same section. Written in our own words; check the manual for your exact model.

Run gas and air auto adjust (UC)

Tankless water heater · Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

Automatic gas and air adjustment inside the combustion adjust menu; takes about 15 minutes. Needed after an LPG conversion, repeated unresolved errors, or replacing the control unit, fan or gas valve.

  1. Enter AU Technical Settings and open the combustion adjust menu
  2. Select UC Auto Adjust
  3. Open hot water taps when Open Taps shows
  4. Wait for the green check mark

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

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. Written in our own words; check the manual for your exact model.

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For licensed technicians. Installer menus, test modes and access codes change settings that affect safety; only use them if you are trained on the appliance and understand the result. Gas, electrical and refrigerant work must be done by a qualified, licensed person, and the manufacturer’s manual for the exact model and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.