Heat pumps · Error codes · Cool Energy
E4Cool Energy · EcoStore all-in-one exhaust-air DHW heat pump
E4 on a Cool Energy EcoStore all-in-one exhaust-air DHW heat pump: Evaporator temperature sensor T3 error
Short answer
On a Cool Energy heat pump, E4 means: Evaporator temperature sensor T3 error. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Evaporator temperature sensor T3 error.
Likely causes:
- Connection between sensor and PCB released or sensor broken.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
What you can check
- Read and note the code shown on the controller display, then contact your installer or service engineer.
What the engineer will check
- Check the named sensor/probe connection at the PCB (loose/oxidised plug).
- Measure sensor resistance against the manufacturer table and replace if faulty.
- Check controller/PCB if sensor is good.
Who to ask for: heat pump controls / electrical.
Certification: Electrical competence.
What you might notice
Sources
- Cool Energy EcoStore Heat Pump Water Heater - manual Rev1 ↗ · Rev1 · page 24-26 (printed) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026