Bosch · Refrigerator Serious

E4 — Defrost / Temperature Sensor Fault

Bosch's official US refrigeration error-code page documents only three entries: E02 (icemaker/ice-water communication), E03 (dispenser UI), and a generic 'E or D' catch-all. A bare 'E4' is not separately documented. The 'defrost / temperature sensor fault' explanation below is not confirmed on Bosch's US consumer page — verify against your model's manual, or treat it per Bosch's generic guidance: power-cycle, and call support if it persists.

Keep using it?
Limited use only
DIY difficulty
Moderate
Verified against
bosch-home.com ↗

How to fix it

  1. Unplug the refrigerator and manually defrost the freezer fully.
  2. Pull the rear freezer panel.
  3. Test the defrost heater for continuity end-to-end.
  4. Test the bimetal/defrost thermostat in its cold state (should be closed).
  5. Test the evaporator thermistor for proper resistance.
  6. If all components test good, suspect the main control board's defrost relay.

Why it happens

Typical signs: E4 on display · Heavy frost on the freezer back wall · Fridge section warming up over time · Loud fan from ice contact

  • Open defrost heater Calrod-style heater has burned open.
  • Failed defrost (bimetal) thermostat Safety thermostat stuck open.
  • Failed evaporator sensor Control never sees termination temperature.
  • Main board defrost relay failure Relay cannot energize the heater.

Replace your water filter

A clogged or overdue water filter is a common cause of low water and ice flow on Bosch refrigerators — they are meant to be changed about every 6 months. The OEM-style filter that fits most Bosch refrigerators is the BORPLFTR10 ($60-75 OEM, $25-35 compatible).

  • Bosch BORPLFTR10 refrigerator water filter OEM water filter
    Amazon →

Not sure which filter fits your model? See the full compatibility guide →

Parts you may need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

  • Bosch refrigerator defrost heater Common replacement
    Amazon →
  • Bosch defrost thermostat / bimetal Common replacement
    Amazon →

More Bosch refrigerator codes

E1 E1 — Fresh-Food Compartment Sensor Fault E10 E10 — Inverter Compressor / Compressor Drive Fault E11 E11 — Display Control Module Fault E12 E12 — Damper Control Fault E2 E2 — Icemaker / Ice-Water System Communication Fault E20 E20 — Defrost Drain Heater / Drain Blockage

All Bosch codes → All refrigerator codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: bosch-home.com.