EE4 on a Grant Aerona: Supply L and N are reversed
Short answer
On a Grant heat pump, EE4 means: Supply L and N are reversed. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Supply L and N are reversed.
Part involved: mains supply polarity.
When it shows: Shown on the ATC controller display.
Likely causes:
- Supply live and neutral reversed.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Not stated.
Manual reset: Not stated.
What you can check
- Note the exact code shown on the controller display and tell your installer or Grant-trained engineer.
- Check the heat pump isolator switch and the consumer-unit breaker/RCD for the heat pump are ON (do not repeatedly reset a tripping breaker).
What the engineer will check
- Check supply polarity at power supply terminal (qualified electrician).
Who to ask for: Heat pump engineer.
Certification: Competent electrician/heating engineer for mains electrical and PCB work (safe isolation; capacitor discharge).
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- Heat pump will not start on the Aerona (1st generation): 1 report
Sources
- Grant Aerona Air Source Heat Pump - Air to Water Heat Pump Range - Installation & User Instructions (DOC.87) ↗ · Rev.05 · page 37 (PDF p41); s13.5-13.6 p36 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026