Bosch Heat-pump E4 Error Code — Meaning & Causes (2026)
Temperature sensor fault — sensor T3, T3L, T4, T5 or TF is out of range. Below: what triggers it and what to check — this code carries no single repair to price. Reviewed July 2026.
What E4 means
Temperature sensor fault — sensor T3, T3L, T4, T5 or TF is out of range.
Likely causes, most common first
- Failed temperature sensor
- Broken wire to the temperature sensor
- Poor connection at the control board
Base: 1 published national repair-cost guide (retrieved 2026-07) · full source registry on the methodology page · Code meaning & causes · Reviewed July 2026
No single repair to price for this code
E4 doesn't point at one failed component, so we don't attach a price module — forcing a repair mapping here would be dishonest. If the code keeps returning, the underlying symptom (not the code) is what gets priced: browse the heat pump repair costs for the problem you're actually seeing.
Codes are universal — your location changes the repair price, never the code's meaning. See the methodology for the exact localization formula and sources.
Reviewed by a Red Seal–certified appliance technician who also holds a Technical Safety BC gas ticket (Gas-C) and an ODS/halocarbon refrigerant ticket (CFC/HCFC/HFC).