Bosch Error Code C1: Flue blockage at start-up (Tankless)
Bosch error code C1 on a tankless water heater means: Flue blockage at start-up. It is also called Bosch diagnostic code C1.
Homeowner? What Bosch code C1 means for you
Call a technician Your tankless water heater is reporting: Flue blockage at start-up. The tankless water heater 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 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 C1 mean?
Heavy blockage was seen at start-up because of too little combustion air; the unit shuts down for safety.
Applies to: Bosch Greentherm T9800 SE 160/199 and T9900 SE 160/199 / i 199 tankless water heaters
Common causes of Bosch code C1
- Blocked intake or exhaust
- Vent too long
- Dirty air filter
Bosch models that use code C1
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 C1: homeowner questions
What does Bosch code C1 mean?
Flue blockage at start-up. Heavy blockage was seen at start-up because of too little combustion air; the unit shuts down for safety.
Is it safe to keep using my tankless water heater with code C1?
It depends on the cause. The tankless water heater 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 C1 myself?
You can try one reset (power off for 30 seconds, then on). If Bosch code C1 comes back, the cause is still there and a licensed technician should check it.
Who can fix Bosch code C1 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
Source: Bosch Greentherm T9800 SE 160/199 installation 6720816815 (06.2023), Table 24 Error code diagnostics, p.65-69; Bosch Greentherm T9900 SE 160/199 | i 199 installation 6 720 813 635 (2024-06), section 9.1 Error code diagnostics, p.68-73. 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.