Bosch Boiler: Move the 3-way valve to centre to drain (function 7.b)
Move the 3-way valve to centre to drain (function 7.b) on a Bosch boiler: 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.
Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis
How to fix move the 3-way valve to centre to drain (function 7.b): step by step
- Open service functions with the service button and scroll with key pad lock / ECO
- Select 7.b, set 01 and save
If the unit shows an error code, look it up: Bosch Boiler codes
Models
ZBR21-3AZBR28-3AZBR35-3AZBR42-3A
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 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.