Er03 on a Cool Energy heat pump: Insufficient water flow
Short answer
On a Cool Energy heat pump, Er03 means: Insufficient water flow. 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: Insufficient water flow.
On the Inverter range CE-iH (R410A, c.2020)
The manual says: Supply Water Probe Fault.
On the Pro Range CE-H (fixed-speed)
The manual says: Water flow switch fault (troubleshooting table 'Error code 03'; not in common code table).
Likely causes:
- Water flow switch faulty.
- Connection cable damaged or disconnected.
- Controller / PC board faulty.
Is it safe?
On the ecoTech DC Inverter (R32 EVI)
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Clears when flow restored (p.33).
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? | 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 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.
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.
What the engineer will check
On the ecoTech DC Inverter (R32 EVI)
- Check water flow rate/flow switch and wiring.
- Check strainer/magnetic filter for blockage.
- Vent air from the system.
- Check circulating pump operation and pipe sizing.
- Check valves/zone valves are open.
Who to ask for: heating / plumbing heat pump installer.
Certification: None specific (unvented/G3 if cylinder work).
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)
- Replace water flow switch; if no flow switch installed check terminal is linked out.
- Replace/reconnect cable.
- Replace PC board/controller.
- Check water flow rate/flow switch and wiring.
- Check strainer/magnetic filter for blockage.
- Vent air from the system.
- Check circulating pump operation and pipe sizing.
- Check valves/zone valves are open.
Who to ask for: heating / plumbing heat pump installer.
Certification: None specific (unvented/G3 if cylinder work).
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 27 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026