Grant A2 Fault Code: Causes, Fixes & Repair Costs
What does the Grant A2 fault code mean?
A2 on a Grant Aerona³ heat pump is a DC current detection error: the inverter's current-measurement circuit on the main PCB has reported a reading outside expectations. The main board continuously measures the DC current feeding the compressor drive — it is how the inverter protects itself and the compressor from overload — and when that measurement fails its plausibility checks, the unit shuts down protectively. Grant's own documentation is blunt about the usual outcome: if the error persists after a restart, the main PCB should be replaced. A one-off A2 after a supply disturbance can clear on a power-cycle; a recurring one is board-level hardware.
General guidance only — not a substitute for professional advice, and not certified by an heat pump engineer. Always have your specific appliance assessed by a qualified professional. Any heat pump work must be carried out by an MCS-certified heat pump engineer. If you notice a refrigerant leak, a burning smell or water leaking from the unit, switch it off at the isolator and call an MCS-certified heat pump engineer. Refrigerant work must be carried out by an F-Gas registered engineer.
Common causes
- Main PCB current-detection circuit fault Common
The measuring shunt or its amplifier on the inverter board fails or drifts — the documented cause, and the reason Grant's remedy is board replacement when the code persists.
- Supply disturbance upsetting the inverter Sometimes
A spike or brownout can trip current detection transiently; this is the case a single power-cycle genuinely cures.
- Compressor drive stress Rare
A compressor working abnormally hard — seizing bearings, refrigerant problems — can drag currents out of range; the engineer rules this out before condemning the board.
How to fix it
- Power-cycle once at the external isolator DIY safe
Switch the heat pump off at its external rotary isolator, wait about three minutes for the inverter capacitors to discharge, and switch back on. One controlled restart is legitimate; if the code returns, leave it for an engineer.
- Have a suitably qualified heat pump engineer complete the documented checks heat pump engineer
The engineer will check the supply voltage, inspect the inverter and compressor current draw, and — per Grant's documentation — replace the main PCB if A2 persists. Work on the sealed refrigerant circuit legally requires an F-Gas registered engineer; your installer or a Grant-accredited (G1) installer is the right call, and Grant UK technical support (01380 736920) can assist with diagnosis.
Parts you may need
- Main PCB (inverter board) · from £300
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£450, depending on the underlying cause.
Frequently asked questions
What does A2 mean on my Grant Aerona³?
The inverter's DC current measurement on the main circuit board has failed its checks, so the heat pump shut down to protect the compressor. Try one power-cycle at the isolator; if A2 returns, Grant's documented remedy is main PCB replacement — an engineer's job.
Can I keep resetting it?
No — current detection is how the inverter protects itself and the compressor. Running with it faulty risks the most expensive components in the unit. One restart, then book the repair.
Is the heating off entirely meanwhile?
The heat pump will not run, so you are on whatever backup your system has (immersion heater or backup boiler if fitted). Mention you have none when booking and a good firm will prioritise the visit.