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Bosch · Tankless water heater

C7 Fan fault

High severity Bosch Greentherm T9800 SEBosch Greentherm T9900 SE

What the control is telling you

The fan is disconnected or damaged.

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

Likely causes

  • Loose fan wiring
  • Failed fan

Test and repair steps

  1. Check the fan wiring.
  2. Hold the power button down roughly 3 s to clear the stored error.
  3. Replace the fan or wiring if it persists.

Models that show this code

6 models in Bosch Greentherm T9800 SE, Bosch Greentherm T9900 SE

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

Other codes on the same units

  • C1 Flue blockage at start-up
  • C2 Flue blockage at start-up
  • C3 Flow sensor sees no recirculation
  • C5 Bypass water valve fault
  • C8 Main water valve fault
  • C9 Barometric pressure sensor damaged
  • E0 Control unit internal error
  • E1 Hot water above 194 F (90 C)

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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. 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.