Er04 on a Cool Energy heat pump: Antifreeze protection
Short answer
On a Cool Energy heat pump, Er04 means: Antifreeze protection. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 3 sources
What it means
On the ecoTech DC Inverter (R32 EVI)
The manual says: Antifreeze protection.
On the Inverter range CE-iH (R410A, c.2020)
The manual says: Return Water Probe Fault.
On the Pro Range CE-H (fixed-speed)
The manual says: Anti-freeze Protection.
When it shows: Outlet water <=2C during antifreeze mode; warns until >=4C (p.24).
Is it safe?
On the ecoTech DC Inverter (R32 EVI)
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
On the Inverter range CE-iH (R410A, c.2020)
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
On the Pro Range CE-H (fixed-speed)
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
What you can check
On the ecoTech DC Inverter (R32 EVI)
- 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.
On the Inverter range CE-iH (R410A, c.2020)
- Read and note the code shown on the controller display, then contact your installer or service engineer.
On the Pro Range CE-H (fixed-speed)
- 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
On the ecoTech DC Inverter (R32 EVI)
- 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.
On the Inverter range CE-iH (R410A, c.2020)
- 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.
On the Pro Range CE-H (fixed-speed)
- 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
- Cool Energy ecoTech Monoblock Series R32 EVI Heat Pump Water Heaters - Installation and Users Guide v2.1 (2022) ↗ · Version 2.1 · page 31 · Reviewed 23 September 2026
- Cool Energy Inverter Monoblock Series Heat Pump Water Heaters - Installation and Users Guide Version 5 ↗ · Version 5 · page 22 · Reviewed 23 September 2026
- Cool Energy Pro Monoblock Series Heat Pump Water Heaters - Installation and Users Guide Version 5 ↗ · Version 5 · page 24-25 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026