Bosch Error Code AtL: Ambient temperature limited (Heat Pump)

Updated October 13, 2026 · by Aurora Star Tech Inc.

Bosch error code AtL on a heat pump means: Ambient temperature limited. It is also called Bosch diagnostic code AtL.

Low severityHeat PumpBosch IDS Light · Bosch IDS Premium Connected

Homeowner? What Bosch code AtL means for you

Usually minor Your heat pump is reporting: Ambient temperature limited. 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 AtL mean?

Operation is restricted because the outdoor temperature is outside the operating range.

Applies to: Bosch IDS Light BOVA15-24/36/60 and IDS Premium Connected BOVA36-20/60-20 R-454B heat pump outdoor units

Common causes of Bosch code AtL

Ambient outside 15-125 F in cooling or -4 to 86 F in heating
Thermostat O/B setting wrong
T4 sensor wiring or reading wrong

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 AtL

BOVA15-24 BOVA15-36 BOVA15-60 BOVA36-20 BOVA60-20

Other Bosch Heat Pump codes

Code	Meaning
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
E7	T5 discharge sensor not reading correctly
E41	T3 temperature sensor fault
E42	T3L temperature sensor fault
E43	T4 temperature sensor fault
E44	T5 temperature sensor fault

All Bosch Heat Pump error codes →

Bosch code AtL: homeowner questions

What does Bosch code AtL mean?

Ambient temperature limited. Operation is restricted because the outdoor temperature is outside the operating range.

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

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

Can I reset Bosch code AtL myself?

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

Who can fix Bosch code AtL 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

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. 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.