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Bosch · Heat pump

E51 Input voltage out of range

High severity Bosch IDS LightBosch IDS Premium Connected

What the control is telling you

The outdoor unit sees supply voltage too high or too low.

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

  • Supply above 270 V or below 172 V
  • Bad board

Test and repair steps

  1. Measure supply voltage it must not exceed 270 V or drop below 172 V; fix the supply or call the utility.
  2. If the supply is good and bus voltage (P-N, CN3) is under 310 V, replace the control board.

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

  • E42 T3L temperature sensor fault
  • E43 T4 temperature sensor fault
  • E44 T5 temperature sensor fault
  • E45 Th temperature sensor fault
  • E52 DC bus voltage out of range
  • E81 EEV coil fault
  • F1 High pressure switch protection
  • F2 System lockout (5 low-pressure trips in 100 minutes)

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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.