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Bosch Mini Split E4 Error Code
Quick answer
E4 means indoor return air temperature sensor error. In plain English, the named temperature or air-quality sensor is not sending a believable reading, so the control cannot trust that part of the system. Advisory Technician Breadth evidence 2 published catalog models on its documented product line. Safe first check Turn the system off with the remote, then power cycle once at the breaker or disconnect if you can do that safely. Do not open covers, unplug sensors, or spray cleaner into the sensor area. Stop point Stop here: electrical or inverter work is technician-only. Do not open panels, te.
Severity: high · DIY difficulty: intermediate
Safety
TBD - must be written per-code before publish
What E4 means
E4 means indoor return air temperature sensor error. In plain English, the named temperature or air-quality sensor is not sending a believable reading, so the control cannot trust that part of the system. Advisory Technician Breadth evidence 2 published catalog models on its documented product line. Safe first check Turn the system off with the remote, then power cycle once at the breaker or disconnect if you can do that safely. Do not open covers, unplug sensors, or spray cleaner into the sensor area. Stop point Stop here: electrical or inverter work is technician-only. Do not open panels, te.
Causes, ranked
Causes not yet documented — verify against the service manual.
Sources
- SplitAtlas manual-sourced reference — verified 2026-08-29