Bosch Mini Split E4 Error Code

What E4 means

E4 means an indoor return-air temperature sensor error on Bosch Climate 5000 systems - the room temperature thermistor (T1) circuit is reading outside its allowed voltage window (below 0.06 V or above 4.94 V), so the control stops the system. Power cycle once; if E4 returns, the sensor connector, the thermistor, or the PCB needs technician service. On Gen 3 the same fault shows as EH 60.

First checks before service

This page currently documents the safe reset triage. If the code returns, use the linked source manual or a qualified technician for code-specific diagnosis.

1. 1. One-time fault event (power disturbance or transient sensor reading) common DIY

   Check: Power-cycle at the breaker/disconnect (or unplug for CPAP), restore, and run the system while watching for the code.

   Fix: If the code does not return after a full run cycle, the fault was transient — monitor, no repair needed.

2. 2. Fault persists after a clean reset occasional pro only

   Check: If the code returns immediately or every session, note the conditions (startup, heating, after rain).

   Fix: A persisting code points at the component the manual assigns to this code — that repair is technician territory.