Er02 on a Cool Energy heat pump: Missing phase
Short answer
On a Cool Energy heat pump, Er02 means: Missing phase. 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: Missing phase.
On the Inverter range CE-iH (R410A, c.2020)
The manual says: Water Tank Probe Fault.
On the Pro Range CE-H (fixed-speed)
The manual says: Phase Stagger.
Likely causes:
- Absent phase, phase rotation or voltage imbalance among the 3 phases.
- Controller or PC board faulty (phase rotation protection damaged).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
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 heat pump's breaker/isolator at the consumer unit is switched on (do not repeatedly reset if it trips).
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 heat pump's breaker/isolator at the consumer unit is switched on (do not repeatedly reset if it trips).
What the engineer will check
On the ecoTech DC Inverter (R32 EVI)
- Check supply voltage, phase presence/rotation and balance.
- Check cabling, terminals and MCB/RCBO sizing.
- Check inverter drive/PFC board.
Who to ask for: heat pump electrical.
Certification: Electrical competence (Part P / qualified electrician).
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 incoming phase rotation with a phase rotation meter.
- Test for absent phase and cable connections.
- Test for voltage imbalance.
- Replace PC board and/or controller.
- Check supply voltage, phase presence/rotation and balance.
- Check cabling, terminals and MCB/RCBO sizing.
- Check inverter drive/PFC board.
Who to ask for: heat pump electrical.
Certification: Electrical competence (Part P / qualified electrician).
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 25 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026