HVACopediaBosch · Boiler
CC Outdoor temperature sensor not recognised
What the control is telling you
The outdoor sensor was expected but is not detected.
Applies to: Bosch Greenstar ZBR 21/28/35/42-3A boilers and ZWB 28/35/42-3A combi boilers
Likely causes
- Open lead or loose connection
- Failed outdoor sensor
Test and repair steps
- Check the outdoor sensor and its wire for breaks.
- Confirm the sensor is wired to terminals A and F; replace if faulty.
Models that show this code
4 models in Bosch Greenstar
Other codes on the same units
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
Source: Bosch Greenstar ZBR/ZWB 21-42-3A service manual 6721853955 (2025-11), Table 38 Faults shown on the display, p.74-75; Greenstar combi 100 p/151 p service manual 6721853953 (2025-11), Table 33. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
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.