Bosch P4 error code

What it means

P4 means compressor drive error. In plain English, the compressor drive is reporting abnormal feedback or load.

Urgency

Likely causes

1. Compressor wiring or phase sequence problem
2. Compressor is starting against abnormal pressure/load
3. Outdoor PCB or inverter drive fault
4. Compressor electrical or mechanical fault

Homeowner fix

Turn the system off and wait at least 3 minutes before one safe reset. If the code returns, do not keep forcing starts.

When to call a pro

Call a licensed HVAC technician if P4 returns after one safe reset or the condition will not clear. Tell them the official source lists P4 as Compressor drive error.

Repair vs replace

Inverter-drive and compressor repairs can be expensive. On older out-of-warranty systems, compare major board or compressor quotes with replacement.

• 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 compressor U/V/W wiring, start history, pressure balance, inverter output, compressor condition, and outdoor PCB. 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; compressor-drive diagnosis. 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 four 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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