Heat pumps · Error codes · Cool Energy
E004Cool Energy · EcoSyn wall-hung exhaust-air DHW heat pump
E004 on a Cool Energy EcoSyn wall-hung exhaust-air DHW heat pump: Freezing - temperature in the heat pump below 4C
Short answer
On a Cool Energy heat pump, E004 means: Freezing - temperature in the heat pump below 4C. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Freezing - temperature in the heat pump below 4C.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
What you can check
- Read and note the code shown on the controller display, then contact your installer or service engineer.
- Check the heating system pressure gauge reading against the value in your handover documents (manufacturer commissioning values: typically 1-2 bar) and that the filling loop is closed.
- Check the outdoor unit/air grilles are not blocked by debris, leaves or snow.
What the engineer will check
- Check glycol concentration/antifreeze protection.
- Check water flow and outlet temperature sensor.
- Check defrost operation.
Who to ask for: heating / plumbing heat pump installer.
Certification: None specific.
What you might notice
Sources
- EcoSyn 80/100 Installation, Operation & Maintenance Manual Rev1.2 ↗ · Rev1.2 · page 23 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026