Grant F5 Fault Code: Causes, Fixes & Repair Costs
What does the Grant F5 fault code mean?
The F5 code appears on your Grant Aerona³ remote controller when the heat pump's control system has detected a problem with either the outdoor fan motor or the outdoor PCB (the circuit board housed in the external unit). A red LED will flash on the controller's on/off switch at the same time. Because the outdoor fan is essential for drawing air across the refrigerant circuit, this fault can cause the unit to stop heating entirely or to run well below its normal efficiency. The code needs to be investigated promptly to avoid further strain on the compressor.
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
- Failed outdoor fan motor Common
The fan motor itself has seized, burned out, or developed a mechanical fault. A failed motor is the most frequent trigger for F5 because the PCB monitors whether the fan is running correctly and raises the fault when it detects no rotation or an unexpected current draw. Wear, moisture ingress, or age-related bearing failure are the usual underlying reasons.
- Faulty fan start capacitor Common
The capacitor gives the fan motor its initial electrical kick to start spinning. When the capacitor degrades or fails, the motor may hum but not rotate, or may fail to start at all. The PCB then registers this as a fan fault and triggers F5. Capacitor failure is common on older or heavily cycled units.
- Debris or ice blocking the fan blades Sometimes
Leaves, twigs, compacted ice, or other debris lodged against the fan blades can prevent them from turning freely. The motor stalls under the load, causing an overcurrent condition that the PCB interprets as a fan fault.
- Loose or damaged wiring between the fan motor and outdoor PCB Sometimes
Vibration over time can work connectors loose, and rodents occasionally damage wiring runs. A broken connection means the PCB cannot send drive voltage to the motor or receive feedback from it, so the fault is logged even if the motor itself is healthy.
- Faulty outdoor PCB Rare
The outdoor PCB is responsible for supplying and regulating voltage to the fan motor. If the board develops a component-level failure, it may stop driving the motor correctly even when the motor is in good condition. This is typically confirmed only after the fan motor and its wiring have been ruled out.
How to fix it
- Switch off and isolate the unit at the external isolator DIY safe
Turn the heat pump off at the Aerona³ remote controller, then switch off the dedicated isolator switch on the wall near the outdoor unit. Wait at least five minutes to allow any residual charge to dissipate before approaching the outdoor unit.
- Clear any visible debris from around and above the outdoor unit DIY safe
Check for leaves, twigs, compacted snow or ice around the unit's casing and intake grilles. Carefully remove any blockages by hand or with a soft brush. Never insert anything into the fan guard. If ice has built up on the fan blades due to a freeze event, allow it to thaw naturally before proceeding.
- Attempt to rotate the fan blade by hand through the fan guard DIY safe
With the unit fully isolated from power, gently try to turn the fan blade through the protective grille using a finger. It should rotate smoothly and quietly with very little resistance. If it feels stiff, grinds, or won't move, this strongly suggests the motor bearings have failed or the motor has seized — note this for the engineer. Do not force it. If it spins freely, the motor itself may be intact and the fault could lie with the capacitor, wiring, or PCB.
- Visually check for obviously damaged or disconnected wiring at the outdoor unit DIY safe
Look through the service panel (without removing it) for any wiring that appears visibly burnt, chewed, or hanging loose. Do not open the electrical enclosure or touch any wiring yourself — this observation is simply useful information to pass on to an engineer.
- Do not attempt to reset the fault code yourself DIY safe
Grant UK advise that fault code resets on the Aerona³ controller should only be carried out by a qualified installer or service engineer. Some codes clear automatically once the underlying fault is resolved, but others require a manual engineer reset. Attempting to reset the code yourself without fixing the root cause can mask the fault and potentially cause further damage.
- Contact an MCS-certified heat pump engineer to diagnose and repair the fault heat pump engineer
An engineer will use the diagnostic sequence recommended in the Aerona³ installation manual: confirming whether the fan motor runs under power, testing the start capacitor, checking drive voltage from the outdoor PCB, and inspecting all wiring connections. Depending on findings, the repair will be a fan motor replacement, capacitor replacement, or outdoor PCB replacement. All of this work involves the electrical systems of the outdoor unit and must be carried out by a qualified professional. Refrigerant circuit components must only be handled by an F-Gas registered engineer.
Parts you may need
- Outdoor fan motor (Aerona³ compatible) · from £150
- Fan start capacitor · from £25
- Outdoor PCB (external control board) · from £220
- Fan motor wiring loom / connector set · from £35
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 £250–£550, depending on the underlying cause.
Frequently asked questions
Can I reset the F5 fault code myself on my Grant Aerona³?
Grant UK strongly advise against homeowners resetting fault codes on the Aerona³ remote controller. Depending on the fault, the code may clear automatically once the underlying problem is fixed, but when a manual reset is needed it should only be done by your installer or a qualified service engineer. Resetting the code without fixing the root cause risks the unit running in a degraded or unsafe state.
Will my Grant warranty cover an F5 repair?
It depends on the age of your unit and whether your annual servicing schedule is up to date. Grant Aerona³ units come with a manufacturer warranty, but this is typically conditional on the heat pump being serviced each year by an authorised engineer. If your service history is current and the component failure is not due to accidental damage or misuse, fan motor and PCB faults may well be covered. Check your warranty documentation or contact Grant UK directly to confirm before booking a repair.
How much does it cost to fix a Grant F5 fault in the UK?
For most homeowners the repair falls in the range of £250–£550 including call-out, parts and labour. A fan capacitor swap is at the lower end; a full fan motor replacement typically costs £300–£500; an outdoor PCB replacement tends to be the most expensive option and can push toward or beyond £600 depending on parts availability and the engineer's rates. If your unit is still under warranty, these costs may be covered entirely.
How can I prevent the F5 fault from recurring?
Annual servicing by an MCS-certified engineer is the most effective preventative step — a service visit includes checking the fan motor's condition, testing the capacitor, inspecting wiring connections, and clearing any debris build-up from the outdoor unit. Between services, keep the area around the outdoor unit clear of leaves and vegetation, and check after heavy snowfall that the unit is not blocked or iced over. Staying on top of the service schedule also protects your manufacturer warranty.