E021 on a CTC control system alarm/information platform: Comm. err. motor protection: HP control card (A5) cannot communicate with the motor protection (A4) (EcoZenith i255/EcoHeat 400 numbering)
Short answer
On a CTC heat pump, E021 means: Comm. err. motor protection: HP control card (A5) cannot communicate with the motor protection (A4) (EcoZenith i255/EcoHeat 400 numbering). The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Comm. err. motor protection: HP control card (A5) cannot communicate with the motor protection (A4) (EcoZenith i255/EcoHeat 400 numbering).
Part involved: motor protection A4 / HP control card A5.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Manual reset: Press "Reset alarm" on the display; a persisting fault must be rectified before it can be reset.
What you can check
- Note the alarm code/text, the product model and serial number and contact your installer.
- Check the heat pump isolator/consumer-unit breakers are on.
What the engineer will check
- Check communication cables and connectors between the named boards.
- Check power supply to the named board.
Who to ask for: heat pump controls / electrical.
Certification: Electrical competence for work inside control panels.
What you might notice
Sources
- CTC EcoZenith i255 Installation and Maintenance Manual (400V 3N~/230V 1N~/230V 3~) ↗ · 162 505 67-9 CR01164 2026-05-10 · page 81 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026