Bosch Error Code C6: Fan not running (Boiler)
Bosch error code C6 on a boiler means: Fan not running. It is also called Bosch diagnostic code C6.
Homeowner? What Bosch code C6 means for you
Call a technician Your boiler is reporting: Fan not running. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Safe things you can check yourself
- Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
- Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
- Look at the pressure gauge on the boiler. If it reads much lower than usual or near zero, or water is leaking, call a technician.
- Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
- Check that the boiler gas valve is open (handle in line with the pipe).
- Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Bosch error code C6 mean?
The control does not get the expected fan response.
Applies to: Bosch Greenstar ZBR 21/28/35/42-3A boilers and ZWB 28/35/42-3A combi boilers
Common causes of Bosch code C6
- Fan wiring fault
- Failed fan
Bosch models that use code C6
ZBR21-3AZBR28-3AZBR35-3AZBR42-3A
Other Bosch Boiler codes
All Bosch Boiler error codes →
Bosch code C6: homeowner questions
What does Bosch code C6 mean?
Fan not running. The control does not get the expected fan response.
Is it safe to keep using my boiler with code C6?
It depends on the cause. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Can I reset Bosch code C6 myself?
You can try one reset (power off for 30 seconds, then on). If Bosch code C6 comes back, the cause is still there and a licensed technician should check it.
Who can fix Bosch code C6 near me?
Aurora Star Tech Inc. repairs Bosch boilers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Boiler Not Heating: What to Check
Troubleshooting guides
- No heat or some zones cold All brands · Boiler
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. 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.