Bosch Error Code CA: Water flow above 9.2 gpm (Tankless)

Updated October 13, 2026 · by Aurora Star Tech Inc.

Bosch error code CA on a tankless water heater means: Water flow above 9.2 gpm. It is also called Bosch diagnostic code CA.

Low severityTankless Water HeaterBosch Greentherm T9800 SE · Bosch Greentherm T9900 SE

Homeowner? What Bosch code CA means for you

Usually minor Your tankless water heater is reporting: Water flow above 9.2 gpm. This code is usually informational or minor. The safe checks below often clear it; call us if it keeps showing up.

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) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does Bosch error code CA mean?

Measured water flow is higher than the unit can handle.

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

Common causes of Bosch code CA

Air in the water circuit
No flow restrictor
Water pressure over 150 psi

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Bosch models that use code CA

Greentherm T9800 SE 160 Greentherm T9800 SE 199 Greentherm T9800 SEC 199 Greentherm T9900 i 199 Greentherm T9900 SE 160 Greentherm T9900 SE 199

Other Bosch Tankless codes

Code	Meaning
C2	Flue blockage at start-up
C3	Flow sensor sees no recirculation
C5	Bypass water valve fault
C7	Fan fault
C8	Main water valve fault
C9	Barometric pressure sensor damaged
CE	Flue blockage during operation (siphon pressure)
CF	Flue blockage during operation (insufficient air)
E0	Control unit internal error
E1	Hot water above 194 F (90 C)
E3	Flue gas temperature too high, burner cut off
E4	Cabinet air too hot, burner cut off

All Bosch Tankless Water Heater error codes →

Bosch code CA: homeowner questions

What does Bosch code CA mean?

Water flow above 9.2 gpm. Measured water flow is higher than the unit can handle.

Is it safe to keep using my tankless water heater with code CA?

Usually yes. Code CA is normally minor, but if it keeps coming back have it checked.

Can I reset Bosch code CA myself?

You can try one reset (power off for 30 seconds, then on). If Bosch code CA comes back, the cause is still there and a licensed technician should check it.

Who can fix Bosch code CA 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.