Grant Aerona3 Heat Pump Problems — Faults & Fixes
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The Grant Aerona3 is a robust air source heat pump, but like any heating system, it can develop faults or performance issues—especially if settings haven't been optimised for your home or if basic maintenance has been overlooked. Most problems fall into a few categories: controller configuration, water pressure loss, refrigerant circuit faults, and defrost system issues. Homeowners often spot trouble through low heat output, alarm codes on the controller, or pressure warnings rather than complete breakdown. This guide walks you through the most common Aerona3 problems and what you can safely check yourself before calling your installer. If you've registered your system with Grant and it's still under warranty, your installer should have direct access to Grant's technical support team—a real advantage when diagnosing tricky faults.
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Most likely cause & what to check
The Grant Aerona3 is a popular UK-manufactured air source heat pump, made by Grant Engineering in Ireland. It is available in 6kW, 10kW, 13kW, and 17kW capacities and uses R32 refrigerant. Grant are well known for their oil boilers and have brought similar UK-focused support to their heat pump range. Manuals and support at grantuk.com/support or call Grant Engineering on 01480 477 799.
Aerona3 not heating: check the AEMS (Advanced Energy Management System) controller settings — the heating curve and flow temperature target may need adjusting for your home's heat loss. The Aerona3's AEMS controller can be complex to configure; an MCS-certified installer familiar with the Grant range should optimise it at commissioning and on subsequent visits.
Low system pressure alarm: the Aerona3 requires 1–2.5 bar water pressure. Repressurise using the filling loop on the associated buffer tank or indoor unit to 1.5 bar. If pressure keeps dropping, there is a leak.
Poor defrost performance: the Aerona3 uses a demand defrost system. If the outdoor unit is icing up heavily and not clearing, there may be a defrost sensor or control fault — contact your installer. In the meantime, ensure airflow around the outdoor unit is not restricted.
Fault codes on the AEMS controller: Grant provide a fault code reference in the AEMS installation manual, downloadable from grantuk.com. Most refrigerant-related codes (R series) require an F-Gas engineer; water circuit codes (W series) may be resolvable by checking pressure and flow.
Grant Aerona3 warranty: 5-year parts and labour warranty when installed by an MCS-certified installer and registered with Grant within 30 days. Grant offer telephone technical support to installers — if you have a fault, your installer should contact Grant's technical team directly.
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Frequently asked questions
My Grant Aerona3 is making a noise and won't heat properly—is it broken?
Not necessarily. Unusual noises often signal a defrost cycle, which is normal. More likely, your heating curve settings need fine-tuning to match your home's heat loss characteristics. Ask your installer to review the AEMS controller settings and adjust the flow temperature target; this resolves most low-heat complaints.
What does the low pressure alarm mean on my Aerona3?
Your system needs water pressure topped up to around 1.5 bar using the filling loop on your buffer tank or indoor unit. If the pressure drops again within a few weeks, you've got a leak somewhere in the pipework and will need an engineer to locate and repair it.
Can I fix Aerona3 fault codes myself?
You can check the AEMS manual on Grant's website for what codes mean. Water circuit codes (W series) sometimes clear if you repressurise the system, but refrigerant codes (R series) absolutely require an F-Gas certified engineer—never attempt those yourself.
My Aerona3 is still under warranty—who should fix it?
Contact your MCS-certified installer first; they should ring Grant's technical support team directly rather than diagnosing blind. Grant honour a 5-year parts and labour warranty on registered systems, so your installer can get advice and parts quickly through the proper channel.
How often does the Aerona3 defrost, and should ice on the outdoor unit worry me?
The Aerona3 uses on-demand defrost triggered by sensors; you shouldn't see heavy ice build-up if it's working properly. Light icing is normal in winter, but thick ice that doesn't clear suggests a sensor or control fault—contact your installer to investigate.