A0 on a Grant heat pump: DC voltage error
Short answer
On a Grant heat pump, A0 means: DC voltage error. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 2 sources
What it means
The manual says: DC voltage error.
Part involved: main PCB, DC supply to fan motor and pump, reactor.
When it shows: Detected by heat pump/controller PCB; error reset type printed as 'Power OFF'.
Likely causes:
- Fan motor fault.
- Fuse CF6/CF7 blown.
- Pump fault.
- Reactor faulty.
- Main PCB faulty.
- Power supply.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: No.
Manual reset: Power OFF: after the cause is corrected, the mains supply must be switched OFF and ON again (engineer).
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).
- Grant advises homeowners NOT to reset Aerona3 fault codes themselves - leave the reset to the engineer.
What the engineer will check
- Operate without fan motor lead wire and check fuse continuity: if same code reappears Main PCB or pump should be replaced; if other codes appear replace fan motor.
- Check fuses CF6/CF7 (model dependent) by tester.
- Operate without pump lead wire: if same code reappears replace Main PCB or fan motor; if other codes appear replace pump.
- Check reactor resistance (0.1 ohm at 20C).
- Check voltage of fan motor and pump on Main PCB.
- Check the power supply.
Who to ask for: Grant-trained (G1) 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
12 owner and engineer reports mention this.
- No heating on the Aerona³ R32: 5 reports
- No hot water on the Aerona³ R32: 4 reports
- Heat pump will not start on the Aerona³ R32: 2 reports
- No heating on the Aerona³ (R410A): 1 report
Sources
- Grant Aerona³ Air to Water High Efficiency Heat Pump Range - Installation and Servicing Instructions (UK DOC 0136) ↗ · Rev 2.4 · page 54 (DOC 0154: 53) · Reviewed 23 September 2026
- Grant UK Aerona³ Air to Water High Efficiency Heat Pump Range - Installation and Servicing Instructions (UK DOC 0109) ↗ · Rev 1.1 · page 53 (IRL DOC 0001: s11.4-11.5, printed pp55-57) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026