When a Grant Aerona3 R32 detects a fault, the red light on the remote controller's ON/OFF switch flashes, a warning icon appears on the screen and a short code, such as FU or A5, shows on the terminal PCB display. This guide uses Grant's installer manual for the HPID6R32, HPID10R32, HPID13R32 and HPID17R32 models, so older Aerona units may use different codes.
If a code keeps coming back, or you are not sure what it means, book an engineer rather than resetting it again. We fix Grant heat pumps across the UK and you can book a heat pump repair online or on 0333 041 5130. For other brands, see our heat pump error codes hub.
Safety first: never open the outdoor unit or touch the wiring inside, as fuses, boards and the compressor carry mains voltage.
Please read first: this guide is here to help you understand what your Grant Aerona heat pump is telling you. Every effort has been made to keep the information accurate, but manufacturers update their manuals and codes can differ between models and software versions, so always check the official Grant Aerona manual for changes before acting on anything here. Do not attempt anything that could be dangerous, and avoid any work that could void your warranty. If in doubt, call a qualified heat pump engineer.
If your Grant Aerona heat pump is not showing a code, or you want to rule out the basics first, our guide to common air source heat pump problems walks through the general checks and matches common faults to error codes across every major brand.
Is it safe to fix a Grant Aerona heat pump fault yourself?
You can safely make basic checks, but the repair itself belongs to an engineer. Clearing airflow, checking the pressure gauge, opening valves and a single reset from the controller are fine for most homeowners.
Grant's own diagnosis for many codes involves fuse checks, voltage readings at the fan and pump, and board replacement. Leave that to someone competent, and never work on live electrics.
Refrigerant work is legally restricted to F-Gas certified engineers, and Grant's manual says it must never be attempted by unqualified people. DIY work inside the unit can also affect your warranty, so check the terms first.
Which Grant Aerona error codes can you check yourself?
A few Aerona3 codes have a sensible first check, mostly those linked to airflow, water flow and controller communication. Check once, reset once, and call us if the code comes back.
| Code | What it means | Safe homeowner check | Stop and call an engineer if |
|---|---|---|---|
| A2, A4 | Excess DC or AC current, unit stopped | Clear leaves, snow or anything blocking the air inlet and outlet | It returns, or follows storms or power dips |
| A5 | Abnormal compressor revolution | Check radiator and zone valves are open and the pressure gauge is in range | It returns after one reset |
| FU | High pressure switch operating | Check valves are open and system pressure is correct. Top up only if you have a filling loop and your manual allows it | It returns after one reset |
| P1 | Pump error | Check pressure and that valves are open | The code stays, as pump checks need a meter |
| C1, C3 | Fan motor error | From outside, look for ice, debris or nests blocking the fan. Do not reach inside | The fan is clear but the code stays |
| C4 | Main board running above 110C | Make sure nothing is stacked against the unit or boxing it in | It returns once the area is clear |
| 740, E8, F5 | Controller or main board communication | Wait a few minutes, as these reset automatically | The code does not clear |
What are the most common Grant Aerona heat pump error codes?
The Aerona3 codes that most often have a fixable cause relate to airflow, water flow, sensors and communication. Causes start with what Grant's manual lists; anything marked general engineering knowledge comes from our experience, not the manual.
A2 and A4: excess current protection
The unit has detected too much DC current (A2) or AC current (A4) and stopped. Grant lists a blocked air inlet or outlet, too much refrigerant, low 230V supply voltage, a momentary power loss such as lightning, and a faulty main board or compressor.
General engineering knowledge: a dirty evaporator coil, foliage near the unit and discharge air looping back into the inlet are common underlying causes.
What to do: Clear the airflow and do one manual reset. If it returns, an engineer should check the supply under load.
A5: abnormal compressor revolution
A5 shares many causes with A2 and A4 and adds a clogged pump or water circuit. In our experience the water side is often the real culprit: a blocked strainer or magnetic filter, sludge, a closed valve or air in the system.
What to do: Check valves and pressure. Persistent sludge problems may need a heat pump powerflush.
FU: high pressure switch operating
Grant gives two causes: outside air recirculating into the unit and a clogged water circuit. Its advice is to compare outgoing and return water temperatures on the monitor display, because a large gap means flow is too low.
General engineering knowledge: sludge, scale, a blocked filter or closed zone valves usually sit behind low flow.
What to do: Check valves and pressure, then reset once. An engineer can read flow (d9) and return (d0) temperatures on the controller to confirm a flow problem.
P1: pump error
The circulating pump, the main board or a clogged water circuit. Grant's test is to check the pump voltage: if it is normal the pump is replaced, and if not the main board is the likely fault.
What to do: Check pressure and valves, then call an engineer for the electrical tests.
A1: discharge temperature error
Either the discharge temperature sensor has failed or refrigerant is leaking. A1 resets automatically, which can hide the problem.
What to do: Because it may point to a gas leak, an F-Gas engineer should check the service valve and pipework.
E4, E5 and C2: temperature sensor faults
E4 is the outgoing water sensor, E5 the return water sensor and C2 the outdoor air sensor. Grant's fix is to test the sensor's resistance against its table and replace it if out of range. General engineering knowledge: the outdoor sensor is exposed to weather, so water ingress or damaged cable is worth ruling out.
What to do: Book an engineer with a meter.
C1 and C3: fan motor errors
C3 is the fan motor error on the 6 and 10 models and the lower fan on the 17 model; C1 is the upper fan on the 17. Grant lists blown fuses (CF6 or CF7), a faulty fan motor and a faulty main board.
What to do: Rule out ice, debris and animals first. Our guide to a frozen outdoor unit covers safe ways to deal with ice. Fuse and voltage checks are engineer work.
C7, 740, E8 and F5: communication faults
C7 is a serial error between the main and controller boards, caused by wiring, a faulty board or a missing earth. 740 and E8 are remote controller communication errors and F5 a main board communication error, all linked to wiring, loose interface cables or board faults.
What to do: These reset automatically once the link is restored. If they persist, an engineer needs to check wiring, DIP switch settings and the earth.
Which error code might you see in common situations?
The table below links everyday problems to codes from Grant's Aerona3 R32 manual. Do the first check, then call us if the code stays.
| Scenario | Codes you may see on a Grant Aerona | First check |
|---|---|---|
| Cold snap and iced outdoor unit | C1, C3, A2, A4, A7 | Keep the unit powered and clear snow from around it. Do not chip ice off the coil |
| Losing pressure or low pressure | P1, A5, FU | Grant has no dedicated pressure code, so read the gauge and look for leaks |
| Radiators lukewarm | FU, A5, E4, E5 | Check radiator and zone valves are open and pressure is correct |
| No hot water | L1, L3 | Check the hot water timer and settings on the controller |
| After a power cut | A0, A2, A4, C8 | Give it a few minutes, then try one reset from the controller |
| Unit noisy or fan not spinning | C1, C3, A0 | From outside, look for ice or debris around the fan |
| After a service or filter clean | P1, A5, FU | Check isolation valves were reopened and pressure is back up |
If pressure keeps dropping, our guide to a heat pump losing pressure explains the usual leak points.
How do you reset a Grant Aerona heat pump?
Grant's manual gives a clear reset: press the minus and plus buttons together for three seconds on the remote controller. The Reset SW button on the terminal PCB does the same, but that sits inside the unit, so leave it to an engineer.
How a code clears depends on its type:
- Automatic reset: A1, A6, A7, A8, C1, C2, C5, C7, E4, E5, L1 to L5, 740, E8 and F5 clear themselves once the fault goes.
- Manual reset: A2, A3, A4, A5, C3, C4, FU, P1 and U1 need the controller reset above.
- Power off: A0, C6, C8, P3 and L0 only clear when the power is switched off, which should follow a repair.
Switching the mains off and on also resets the unit, but Grant says this is not recommended. Resetting repeatedly without fixing the cause is a bad idea, as each restart can strain the compressor and hide a worsening fault.
Grant Aerona error code list
This list covers every outdoor unit and controller code in Grant's Aerona3 R32 installer manual. Other Aerona models may differ, so check your manual. Note that Grant's E8 is a communication fault, not a flow fault as on some other brands.
| Code | Meaning | Who should fix |
|---|---|---|
| A0 | DC voltage error | Engineer |
| A1 | Discharge temperature error, sensor or gas leak | F-Gas engineer |
| A2, A4 | Excess DC or AC current protection | Homeowner check, then engineer |
| A3 | CT disconnection | Engineer |
| A5 | Abnormal compressor revolution | Homeowner check, then engineer |
| A6, A7, A8 | Suction, defrost or discharge temperature sensor | Engineer |
| C1, C3 | Fan motor error | Homeowner check, then engineer |
| C2 | Outdoor temperature sensor | Engineer |
| C4 | Main board temperature above 110C | Homeowner check, then engineer |
| C5, C6, C8 | Main board sensor or main board error | Engineer |
| C7 | Controller board serial error | Engineer |
| E4, E5 | Outgoing or return water temperature sensor | Engineer |
| FU | High pressure switch operating | Homeowner check, then engineer |
| P1 | Pump error | Homeowner check, then engineer |
| P3 | High pressure switch error (17 model) | F-Gas engineer |
| U1 | Compressor overheat relay (17 model) | F-Gas engineer |
| L0 | Controller EEPROM error | Engineer |
| L1 to L4 | Hot water, outdoor, thermal store or mix water sensor | Engineer |
| L5 | Humidity sensor error | Engineer |
| 740, E8 | Remote controller communication error | Homeowner check, then engineer |
| F5 | Main board communication error | Engineer |
Where can you find the official Grant Aerona manual?
Grant publishes its Aerona3 R32 installer manual as a free PDF on its UK website. Its manuals library also holds the user manual and controller instructions.
- Grant Aerona3 R32 installer manual, DOC 0136 Rev 2.4, February 2024 (PDF)
- Grant UK manuals and brochures library
Need help with a Grant Aerona heat pump fault?
We repair Grant Aerona heat pumps across the UK, whether it is a single stubborn code or a system that has stopped. Our F-Gas certified engineers carry out full fault diagnosis and Grant heat pump repairs, backed by a 12-month guarantee.
If you are without heating in cold weather, our emergency heat pump repair team offers same-day visits where possible. See our Grant heat pump page for the models we cover, or our Grant Aerona review for a closer look at the range.
Grant's own service schedule covers the evaporator, condensate drain, expansion vessel, magnetic filter and connections, which is why an annual heat pump service prevents many of these codes. Our cover plans combine servicing and repairs. Contact us or call 0333 041 5130.
Frequently asked questions
Does a Grant Aerona store past error codes?
Yes. The unit keeps its last 10 codes, newest first, and an engineer can view them from the terminal PCB. That history helps spot a pattern, such as repeated FU faults that point to a flow problem.
Will an error code void my Grant warranty?
A code itself does not affect your warranty; it is the unit protecting itself. Problems usually come from unqualified repairs or missed servicing, so check your warranty terms.
Does an A5 or U1 code mean the compressor has failed?
Not necessarily. A5 is often caused by a clogged pump or water circuit, and U1 can be a relay or leak issue. Our guide to heat pump compressor problems covers the signs of a genuine failure.
Why is my Grant heat pump not heating but showing no code?
Grant's manual lists a "water not getting warm" fault with no code, linked to a blown fuse, the 4-way valve, the defrost heater, sensors, gas leakage, a clogged water circuit and short cycling from poor air circulation. Our guide to a heat pump not heating walks through the checks.
What can I check before paying for a call-out?
Confirm the unit has power, airflow around it is clear and the controller settings have not changed. Then check valves are open and the pressure gauge reads normally, and note the code before you call.
