A5 on a Grant heat pump: Abnormal revolution of compressor
Short answer
On a Grant heat pump, A5 means: Abnormal revolution of compressor. 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: Abnormal revolution of compressor.
Part involved: compressor / pump / water circuit / fuse CF6.
When it shows: Detected by heat pump/controller PCB; error reset type printed as 'Manual'.
Likely causes:
- Unreasonable operation under overload (blocked air inlet/outlet, excess gas).
- Drop of power voltage (incl. during operation).
- Fuse CF6 blown.
- Clogged water: pump and/or water circuit.
- Momentary stop of power (lightning).
- Compressor or Main PCB faulty.
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: Manual: engineer presses - and + on the remote controller together for 3 s, or Reset SW on the Terminal PCB (mains OFF/ON possible but not recommended).
What you can check
- Note the exact code shown on the controller display and tell your installer or Grant-trained engineer.
- Check the outdoor unit air inlet and fan outlet are not blocked by leaves, snow, ice or stored objects.
- Check the heating system pressure gauge (if one is fitted) and report a low reading to your installer; make sure the filling loop valves are closed.
- 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
- Check the place of installation for blockage of air inlet & outlet.
- Check excess gas.
- Check power voltage (230V) including during operation.
- Check Fuse CF6 continuity by tester; if blown replace Main PCB.
- Check the pump and water circuit; remove blockage then restart.
- Otherwise replace compressor.
Who to ask for: Grant-trained (G1) heat pump engineer.
Certification: F-gas certified refrigeration engineer (refrigerant circuit work).
What you might notice
What owners and engineers report
7 owner and engineer reports mention this.
- No heating on the Aerona³ R32: 5 reports
- Keeps stopping / cutting out on the Aerona³ R32: 1 report
- 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 55 (DOC 0154: 54) · 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 54 (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