HVACopedia

Bosch · Heat pump

E43 T4 temperature sensor fault

Medium severity Bosch IDS LightBosch IDS Premium Connected

What the control is telling you

The T4 sensor on the outdoor unit reads open or shorted.

Applies to: Bosch IDS Light BOVA15-24/36/60 and IDS Premium Connected BOVA36-20/60-20 R-454B heat pump outdoor units

Likely causes

  • Open or shorted sensor
  • Loose connection at CN23

Test and repair steps

  1. Warning: Switch off power and wait 3 minutes before measuring resistance or touching boards.
  2. Check the T4 connection at CN23.
  3. Test T4 for open or short and replace it if failed.
  4. Replace the control board if the sensor is good.

Models that show this code

5 models in Bosch IDS Light, Bosch IDS Premium Connected

BOVA15-24BOVA15-36BOVA15-60BOVA36-20BOVA60-20

Other codes on the same units

  • C3 T3 coil sensor not reading correctly in cooling
  • E7 T5 discharge sensor not reading correctly
  • E41 T3 temperature sensor fault
  • E42 T3L temperature sensor fault
  • E44 T5 temperature sensor fault
  • E45 Th temperature sensor fault
  • E51 Input voltage out of range
  • E52 DC bus voltage out of range

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.

Open the app

Source: Bosch IDS Light installation BTC 762003308 D (02.2025), Fault Code Table 23 and 17.12 Error Code Troubleshooting, p.42-59; Bosch IDS Premium Connected installation BTC 762003301 D (02.2025), Fault Code Table 22 and 18.12 Error Code Troubleshooting. 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.