Bosch Error Code A: Oil return in progress (Heat Pump)

Updated October 15, 2026 · by Aurora Star Tech Inc.

Bosch error code A on a heat pump means: Oil return in progress. It is also called Bosch diagnostic code A.

Low severityHeat PumpBosch IDS 2.0

Homeowner? What Bosch code A means for you

Usually minor Your heat pump is reporting: Oil return in progress. This code is usually informational or minor. The safe checks below often clear it; call us if it keeps showing up.

Safe things you can check yourself

Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
Check both breakers and the outdoor disconnect box beside the outdoor unit; all should be ON.
Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
In winter, keep snow and ice off and away from the outdoor unit. A short defrost cycle with steam is normal.
Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.

Call (647) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does Bosch error code A mean?

During oil return operation the display shows A followed by two digits, which are the compressor frequency in Hz. The unit does this on its own to bring oil back to the compressor. Normal.

Applies to: BOVA IDS 2.0 heat pumps

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Bosch models that use code A

BOVA-36HDN1-M20G BOVA-60HDN1-M20G

Other Bosch Heat Pump codes

Code	Meaning
AtL	Ambient temperature limited
b2	Indoor T2 sensor fault
b3	Indoor refrigerant sensor hardware fault
b4	Indoor refrigerant sensor communication fault
b5	Indoor to outdoor communication fault
b7	R-454B refrigerant leak protection
b8	Refrigerant sensor past service life
C3	T3 coil sensor not reading correctly in cooling
Check button	Point check - read system values on the board display
dF	Defrost in progress
E7	T5 discharge sensor not reading correctly
E41	T3 temperature sensor fault

All Bosch Heat Pump error codes →

Bosch code A: homeowner questions

What does Bosch code A mean?

Oil return in progress. During oil return operation the display shows A followed by two digits, which are the compressor frequency in Hz. The unit does this on its own to bring oil back to the compressor. Normal.

Is it safe to keep using my heat pump with code A?

Usually yes. Code A is normally minor, but if it keeps coming back have it checked.

Can I reset Bosch code A myself?

You can try one reset (power off for 30 seconds, then on). If Bosch code A comes back, the cause is still there and a licensed technician should check it.

Who can fix Bosch code A near me?

Aurora Star Tech Inc. repairs Bosch heat pumps in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.

Homeowner help: AC Running But Not Cooling: What to Check · Heat Pump Not Heating or Blowing Cold Air

Troubleshooting guides

Force cooling for charging with the FORCE button Bosch · Heat Pump
Pair the gateway by Bluetooth (Connect button) Bosch · Heat Pump
Read system values with the CHECK button (point check) Bosch · Heat Pump
Restart the gateway (Reset button) Bosch · Heat Pump
Run the gateway diagnostic (Factory + Connect buttons) Bosch · Heat Pump
Start a manual defrost test (hold FORCE 6 s) Bosch · Heat Pump

Source: Bosch IDS 2.0 service Rev3 (07.2021), 10.2.2 Oil Return Operation p.31-32. Written in our own words as a summary; always check the original manual.

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.