Most UK domestic air conditioning Wi-Fi modules use 2.4 GHz, not the 5 GHz network your phone prefers. Thick brick, a router in the hallway, and a mesh node that blends both bands cause the setup to fail while the infrared remote still works. You can separate the 2.4 GHz name in the router, stand near the indoor unit for setup, and forget the network in the app once. Do not open the indoor electrical cover to reseat a dongle. If there is no Wi-Fi hardware on that model, an app will never connect. An F-gas engineer or the manufacturer's installer fits adapters that live inside the unit. Do not buy a random plug-in gadget, and do not open the gas circuit for a network problem.
The phone is on 5 GHz. The split is not
Phone setups often jump onto 5 GHz because it is faster for video. The air conditioner cannot see that band on a large share of current UK wall units. The phone can use 5 GHz and can roam. Many split modules are 2.4 GHz only and have a weak aerial behind metal. Log into the router and give 2.4 GHz its own name, then point the app at that name. During setup, disable a VPN on the phone and stand in the same room as the indoor unit.
Brick, a cupboard router, and a mesh with two names
Victorian brick and a consumer unit cupboard around the router will drop 2.4 GHz as well. A mesh puck nearer the indoor unit is a household fix. Extenders that broadcast a second hidden name confuse setup. Do not send your Wi-Fi password to anyone. Say only whether the phone can see 2.4 GHz beside the unit.
An adapter the original job never included
Some indoors have Wi-Fi built in. Others need a matching interface tucked into the electrical section. If the original quote never mentioned an adapter, the fascia will not grow one because an app was installed. Look for a Wi-Fi mark on the model sticker or the manual's feature list. Do not prize the cover off to check. Energy Saving Trust's air-to-air page describes the heat pump. It does not add a Wi-Fi module.
The infrared handset still runs the room
The infrared remote is the control that should still run cool, heat and fan. Use it. A failed network is not a failed compressor. If the remote works, you can live without the app until setup is sorted. Wi-Fi is convenience. Cooling and heating do not depend on the router. Fix Wi-Fi when you want schedules. Do not let a network fault talk you into a refrigerant repair.
A smart plug is not a controller
Cutting mains power with a smart plug is a bad way to control a compressor. It skips the proper delay and can damage the unit. Use the remote or a proper interface. HSE electricity guidance is the backdrop for not improvising with the supply.
When another setup wizard is the wrong response
If 2.4 GHz is solid for a phone in that room, the password is right, and the unit still drops out or never enters setup, stop repeating the wizard. Book an engineer who knows that brand's interface. Replacing an internal adapter means isolating the unit and opening the electrical side. That is not a user panel. GOV.UK certification applies to the company if they are working on the refrigerant equipment. If the unit also trips, smells of burning, or will not cool, treat those as the main fault and mention Wi-Fi second. Do not bridge the module. Do not flash unofficial firmware. Refrigerant work is unrelated unless a separate performance fault exists, and even then only a certified company handles the gas. Describe the network symptom: cannot see the unit, joins then drops, or no Wi-Fi mark on the indoor unit at all. Say whether the infrared remote still cools or heats.
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.