Grant 740 Fault Code: Causes, Fixes & Repair Costs
What does the Grant 740 fault code mean?
Fault code 740 appears on the display or terminal PCB of certain Grant heat pump models and is believed to relate to an inverter drive, compressor protection, or electrical fault within the refrigerant circuit's drive electronics. Grant's publicly documented fault codes for the Aerona³ range typically use an alphanumeric format (such as P1 or E5), so a purely numeric three-digit code like 740 may originate from the terminal PCB's internal alarm log, a newer firmware version, or the Grant Aerona 290 (R290) range. If you are seeing this code, cross-reference your specific model's installation manual or contact Grant UK technical support (01380 736920) to confirm its exact meaning for your unit. Regardless of the precise trigger, a 700-series code will usually cause the heat pump to shut down as a protective measure to prevent damage to the compressor or inverter module.
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
- Insufficient water flow through the heating circuit Common
If the system pressure has dropped, a valve is partially closed, there is an airlock, or the circulation pump is struggling, the heat pump's flow protection logic can trigger a shutdown. The built-in flow switch monitors circulation rate and will cut the compressor to prevent damage if flow falls below the minimum threshold. This is one of the most frequent triggers for a serious fault code on Grant systems.
- Blocked plate heat exchanger or dirty magnetic filter Common
Sludge, scale, or debris in the heating circuit can gradually restrict flow through the plate heat exchanger. Even small particles that pass through the magnetic filter can accumulate and reduce heat transfer efficiency significantly, eventually causing the unit to shut down on a protection fault.
- Inverter drive or IPM (Intelligent Power Module) fault Sometimes
700-series codes on Grant systems are architecturally associated with the DC inverter drive electronics that vary compressor and fan speed. A fault in this circuit — whether due to overheating, a voltage spike, or component degradation — will cause a full system lockout and requires specialist diagnosis.
- Refrigerant circuit anomaly Sometimes
A low refrigerant charge, a partially blocked expansion valve, or a faulty high-pressure sensor can cause abnormal operating pressures that the control system interprets as a protection event. Any work on the sealed refrigerant circuit must be carried out by an F-Gas registered engineer.
- Main PCB or controller board failure Rare
The controller PCB coordinates temperature sensors, defrost cycles, pump output and compressor communication. If this board develops a fault — due to age, moisture ingress or a power surge — it can generate spurious or genuine fault codes and cause the system to shut down.
How to fix it
- Check system pressure at the filling loop gauge DIY safe
Look at the pressure gauge on your heating system (typically mounted near the heat pump or indoor unit). Normal operating pressure is usually between 1.0 and 2.0 bar. If it reads below 1.0 bar, the system may need topping up via the filling loop. Consult your user manual for the correct procedure for your specific installation, or ask your installer if you are unsure.
- Inspect the outdoor unit for obstructions DIY safe
Go outside and check that the outdoor unit's air inlet and outlet grilles are clear of leaves, compacted snow, ice, or other debris. Restricted airflow can cause the unit to overheat and trigger protection faults. Clear any obvious blockages gently by hand — do not use tools near the fan blades.
- Check for a tripped MCB on your consumer unit DIY safe
Go to your consumer unit (fuse board) and check whether the MCB labelled for the heat pump has tripped. If it has, switch it back on once. If it trips again immediately, do not reset it again — this indicates an electrical fault that requires an engineer.
- Attempt a controlled restart via the external isolator DIY safe
Grant UK advise that some fault codes can only be cleared by switching off the electrical supply to the heat pump at the external isolator, waiting at least two minutes, and then switching it back on. If the code reappears after restart, do not continue to reset the unit repeatedly as this can cause further damage.
- Do not attempt to reset the fault code on the controller yourself heat pump engineer
Grant UK specifically advise that homeowners should not manually reset fault codes on the Aerona remote controller. Some codes reset automatically once the underlying fault is resolved, while others must be reset by a trained engineer. Repeated resets without fixing the root cause can mask a serious fault and risk compressor damage.
- Have an MCS-certified engineer inspect the circulation pump and flow sensor heat pump engineer
An engineer will check whether the circulation pump is receiving power and delivering adequate flow. If the pump is energised but not moving water, it likely needs replacing. If flow is present but the fault persists, the flow sensor itself may be faulty. Either component requires professional replacement.
- Have an engineer inspect and clean the magnetic filter and plate heat exchanger heat pump engineer
A qualified engineer can remove, inspect and clean the magnetic filter cartridge and assess whether the plate heat exchanger is blocked with scale or sludge. A power flush or chemical clean may be recommended if the system water is heavily contaminated.
- Have an F-Gas registered engineer assess the refrigerant circuit and inverter board heat pump engineer
If water-side causes have been ruled out, the fault likely lies within the refrigerant circuit (charge level, expansion valve, high-pressure sensor) or the inverter drive electronics (IPM module or main PCB). All refrigerant work is legally restricted to F-Gas registered engineers. PCB and inverter board replacement also requires a qualified heat pump engineer to ensure correct commissioning.
Parts you may need
- Grant Aerona³ circulation pump · from £180
- Water flow sensor / flow switch · from £45
- Grant Aerona³ main controller PCB · from £320
- Magnetic filter cartridge (replacement) · from £35
- Inverter / IPM module · from £280
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–£550, depending on the underlying cause.
Frequently asked questions
Is fault code 740 listed in the Grant Aerona³ manual?
Fault code 740 does not appear in any publicly available Grant Aerona³ manual. Grant's Aerona³ range typically uses alphanumeric codes (e.g. P1, E5, A0), so a three-digit numeric code like 740 may come from the terminal PCB's internal alarm log, a specific firmware version, or the newer Aerona 290 (R290) range. The full fault code tables are only included in the installation and servicing manual supplied with the unit. If you cannot locate your manual, contact Grant UK technical support on 01380 736920 with your model number and serial number.
Can I reset fault code 740 myself?
Grant UK advise homeowners not to manually reset fault codes on the Aerona remote controller. You can safely try switching the heat pump off at the external isolator, waiting two minutes, and switching it back on — this is the one homeowner-safe reset method. If the code returns after this, you should contact your installer or an MCS-certified heat pump engineer rather than continuing to reset the unit, as repeated resets without fixing the underlying problem can cause compressor damage.
How much will it cost to fix a Grant heat pump showing a 740 fault?
For the most common root causes — low system pressure, a failing circulation pump, a dirty filter, or a faulty flow sensor — repair costs typically fall between £150 and £550 including call-out, parts and labour. If the fault turns out to involve the main PCB or inverter module, costs can rise to £600–£900. In the unlikely worst-case scenario of compressor failure, replacement can exceed £1,500–£2,500, which is why early diagnosis matters. Costs in London and the South East tend to run 10–15% higher.
Does my Grant heat pump need an annual service to stay under warranty?
Yes. Grant UK require annual servicing to maintain the product guarantee. A typical service costs £150–£300 and includes inspecting the magnetic filter, checking system pressure and water quality, verifying refrigerant operating pressures, and testing all sensors and controls. Regular servicing is also the best way to catch developing faults — such as those that can lead to a 700-series shutdown code — before they cause expensive component failures.