Er27 on a Cool Energy heat pump: Outlet water temperature sensor fault
Short answer
On a Cool Energy heat pump, Er27 means: Outlet water temperature sensor fault. 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: Outlet water temperature sensor fault.
On the Inverter range CE-iH (R410A, c.2020)
The manual says: Low Pressure Fault.
When it shows: Low pressure on compressor; not detected during defrost or first 5 min after start (p.21).
On the Pro Range CE-H (fixed-speed)
The manual says: Faulty outlet water temp sensor.
Likely causes:
- Outlet water temperature sensor faulty.
- Sensor plug disconnected/oxidised.
- Controller/PC board faulty.
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 |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Resumes 3 min after reset.
Manual reset: Permanently disabled after 3 occurrences within 1 hour.
On the Pro Range CE-H (fixed-speed)
| 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.
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.
- 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 Pro Range CE-H (fixed-speed)
- Read and note the code shown on the controller display, then contact your installer or service engineer.
What the engineer will check
On the ecoTech DC Inverter (R32 EVI)
- 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 Inverter range CE-iH (R410A, c.2020)
- Check water flow first (high pressure is often caused by low flow).
- Check refrigerant pressures/temperatures with gauges (F-gas qualified).
- Check for refrigerant leak or blockage, EEV operation and pressure switches/transducers.
Who to ask for: refrigeration / F-gas heat pump engineer.
Certification: F-gas certification (Category I) for refrigerant circuit work.
On the Pro Range CE-H (fixed-speed)
- Replace or reconnect/clean sensor.
- Replace controller/PC board.
- 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 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