Bosch Error Code b4: Indoor refrigerant sensor communication fault (Heat Pump)
Bosch error code b4 on a heat pump means: Indoor refrigerant sensor communication fault. It is also called Bosch diagnostic code b4.
Homeowner? What Bosch code b4 means for you
Check, then call Your heat pump is reporting: Indoor refrigerant sensor communication fault. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
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) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Bosch error code b4 mean?
The control cannot communicate with the A2L sensor.
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 b4
- Sensor unplugged or not seated
- Failed sensor
Bosch models that use code b4
BOVA15-24BOVA15-36BOVA15-60BOVA36-20BOVA60-20
Other Bosch Heat Pump codes
All Bosch Heat Pump error codes →
Bosch code b4: homeowner questions
What does Bosch code b4 mean?
Indoor refrigerant sensor communication fault. The control cannot communicate with the A2L sensor.
Is it safe to keep using my heat pump with code b4?
It depends on the cause. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Can I reset Bosch code b4 myself?
You can try one reset (power off for 30 seconds, then on). If Bosch code b4 comes back, the cause is still there and a licensed technician should check it.
Who can fix Bosch code b4 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.