Bosch P3 error code

What it means

P3 means outdoor unit low temperature lockout. In plain English, outdoor temperature is outside the range the unit allows, or the outdoor unit is reading it that way.

Urgency

Likely causes

1. Outdoor temperature is below or above the allowed operating range
2. Outdoor unit has poor ventilation or is installed in a heat-trapping location
3. Outdoor ambient sensor is loose, failed, or misreading
4. Outdoor control board is misreading the sensor

Homeowner fix

Wait for outdoor conditions to improve. Make sure the outdoor unit has open air around it and is not packed with debris or snow; do not remove panels.

When to call a pro

Call a licensed HVAC technician if P3 returns after one safe reset or the condition will not clear. Tell them the official source lists P3 as Outdoor unit low temperature lockout.

Repair vs replace

This is usually an operating-limit condition. Service is needed only if the unit is misreading normal outdoor conditions.

• Bosch Climate 5000 A/B legacy R-410A 9,000 BTU Regular (BMS500-AAU009-1AHWXB / BMS500-AAS009-1CSXRA)

  Climate 5000 A/B legacy R-410A

• Bosch Climate 5000 A/B legacy R-410A 12,000 BTU Regular (BMS500-AAU012-1AHWXB / BMS500-AAS012-1CSXRA)

  Climate 5000 A/B legacy R-410A

• Bosch Climate 5000 Gen 4 R-454B 6,000 BTU Regular (BMS500-AAU006-1AHWXD / BMS500-AAS009-1CSXRD)

  Climate 5000 Gen 4

• Bosch Climate 5000 Gen 4 R-454B 9,000 BTU Max Performance (BMS500-AAU009-1AHWXD / BMS500-AAS009-1CSXHD)

  Climate 5000 Gen 4

For your technician

Technician note: verify outdoor ambient conditions, OAT sensor connection/resistance, outdoor ventilation, installation clearances, and PCB input. Source: Bosch Climate 5000 G2 A/B IDU service manual Table 14 and ODU service manual Table 12; supporting diagnosis sections where listed; Table 12/Table 14. Page context: Bosch maps this display to the Climate 5000 A/B legacy R-410A line; source: Bosch Home Comfort official Climate 5000 G2/A-B Ductless AC-HP IDU and ODU Service Manuals, wall-mounted error-code tables and diagnosis sections; display convention: match the letter P and three marker exactly before comparing neighboring codes.

Which systems show it

Climate 5000 A/B legacy R-410A

Related troubleshooting

Use the symptom guide alongside the exact display code if the unit is flashing, cycling, or showing comfort symptoms.

Related codes

Source

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