Bosch · Air handler

4 flashes Refrigerant sensor communication fault

Medium severity Bosch IDS Plus/Premium air handler

What the control is telling you

No communication with the A2L sensor.

Applies to: Bosch IDS Plus/Premium BIVA20 R-454B air handlers (2-5 ton)

Likely causes

Sensor unplugged
Failed sensor

Test and repair steps

Reseat the sensor.
Replace it and repower if needed.

Models that show this code

4 models in Bosch IDS Plus/Premium air handler

BIVA20-24BIVA20-36BIVA20-48BIVA20-60

Other codes on the same units

2 flashes Indoor T2 sensor fault
3 flashes Refrigerant sensor fault
5 flashes Indoor-to-outdoor communication fault
8 flashes Refrigerant sensor past service life
Continuous flashing R-454B refrigerant leak protection
LED off Power supply failure

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Source: Bosch IDS Plus/Premium air handler BIVA20 installation BTC 762003302 C (10.2024), section 13 LED Flashing Troubleshooting, p.49-50. 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.