What a professional air conditioning service includes, which jobs owners can do themselves, how often systems need attention through the year, and the legal checks that apply to larger installations.
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Air conditioning rarely breaks down out of the blue. In the months before it fails, a system is usually working harder than it should. The filters clog and the coils gather dust. Drains silt up a little at a time, and fan bearings wear. Each of those costs a bit of efficiency, and between them they shorten the life of the equipment. Regular maintenance stops those small problems turning into expensive ones.
This guide covers what proper maintenance looks like for UK split, multi-split, ducted and cassette systems. We split out the jobs you can do yourself from the ones that need a qualified engineer and say how often each should happen. We also cover the legal requirements for larger commercial systems.
A professional service means inspecting, cleaning and testing both the indoor and outdoor units in a set order. The exact checklist varies with the system, but a thorough visit should include the following.
At the end of a useful service you should get a short report covering what was found and what was done, plus anything to keep an eye on or plan for. If the engineer can't tell you which operating readings they took, you probably had a wipe-down and not a service.
Some maintenance is easy enough to do yourself, and it makes a real difference between services. Leave anything that involves refrigerant, electrics or taking the unit apart to a qualified engineer.
| Task | Who | How often |
|---|---|---|
| Clean indoor unit filters | Owner | Every few weeks in heavy use; at least monthly in summer |
| Wipe the indoor unit casing and louvres | Owner | Monthly |
| Keep the outdoor unit clear of leaves and plants | Owner | Check monthly, especially in autumn |
| Watch for drips, odours and unusual noise | Owner | Ongoing |
| Deep clean of coils, fan and drain | Engineer | At each service |
| Electrical and control checks | Engineer | At each service |
| Refrigerant pressure checks and leak testing | F-Gas qualified engineer | At each service; legally set intervals for larger systems |
If you only do one maintenance job yourself, make it this one. Clogged filters cut the airflow, so the unit has to work harder and cools less well, and the indoor coil can end up icing over.
Some units also have secondary filters, such as carbon or fine particle filters, which are replaced rather than washed. Your manual or engineer will tell you how often. On cassette and ducted units the filters sit in ceiling grilles, and an engineer can often reach those more safely than you can.
With a concealed system, the dirt is hidden too. A ducted unit in a loft or ceiling void has its filters behind a return air grille, and whatever dust gets past them settles in the ductwork and on the coil, out of sight. Cassettes in offices and shops pull air from busy, often dusty spaces. They drain condensate through a built-in pump, and that pump can fail without any fuss until a ceiling tile starts to stain.
On these systems the engineer should check the return air filters and grilles and look at the access panels in the ceiling. They should also test the condensate pump (and its alarm or safety switch, if there is one) and make sure the airflow at each grille is still balanced. Cassettes above sales floors or kitchens often need their filters cleaning more often than the service interval allows, so agree who will do that between visits.
For most homes, one professional service a year is enough, as long as the filters are cleaned regularly in between. Commercial systems, and anything that runs long hours, do better with more frequent visits. Every six months is common, and busier sites such as restaurants, gyms and server rooms are often serviced quarterly.
A lot of people book a domestic service in spring so the system is ready for summer. You can have it done at any time of year, though, and it's usually easier to get a date outside the busy season. Systems used mainly for heating in winter need servicing just as much as those used for cooling. That's worth bearing in mind further north, and our Edinburgh air conditioning page has local details.
Under the F-Gas regulations, systems containing refrigerant at or above 5 tonnes of CO2-equivalent must be leak checked at set intervals by a qualified engineer, with records kept. The required frequency increases with the size of the charge. For R32, 5 tonnes CO2-equivalent works out at roughly 7.4kg of refrigerant, so most single domestic splits fall below the threshold, while large multi-split and VRF systems in commercial buildings often exceed it.
Air conditioning systems with a combined cooling output over 12kW in a building must have a TM44 energy inspection at least every 5 years. It's separate from routine servicing. The inspection looks at how efficient the system is and how it's controlled, then recommends improvements. Business owners will find both sets of obligations explained on our commercial air conditioning installation page.
A damp or stale smell when the unit first runs usually means something is growing on the indoor coil or in the drain tray. Cleaning the filters won't fix it. The coil and drain need a proper clean and treatment, which an engineer from UK Aircon can carry out as part of a service.
Is the room taking noticeably longer to reach temperature? Dirty filters, a clogged coil or a dusty fan wheel are the usual culprits. Leave restricted airflow long enough and the coil can freeze.
Water marks below the unit mean the condensate drain is partly blocked or the pump is struggling. Sorting it out during a service costs far less than repairing a stained ceiling or damaged plaster later.
Rattles, squeals or a change in how the outdoor unit sounds often mean loose panels, debris or worn fan bearings. Catch them early and they're minor fixes. If a unit has already stopped working, our guide to air conditioning repair explains how faults are diagnosed.
A system that's working harder uses more electricity to keep you just as comfortable. If your bills have crept up and you haven't changed how you use it, start with a service. Our article on air conditioning running costs shows how to estimate what a unit should use.
Modern splits are heat pumps, so plenty of UK systems run all year. A simple routine through the seasons keeps them ready for whichever mode they're in.
Book the annual service, clean filters, and check the outdoor unit is clear before the first warm spell.
Clean filters every few weeks during heavy use and keep an eye on drips and drainage.
Clear fallen leaves from around the outdoor unit and test heating mode before the weather turns.
Keep snow and debris away from the outdoor unit. It needs free airflow to heat efficiently.
Skipping maintenance rarely saves money. Dirty filters and coils mean the system draws more power for the same output, so running costs go up. Parts run hotter and work harder, which shortens the life of the fans and, most expensively, the compressor. Small refrigerant leaks go unnoticed and performance drops further. On top of that, many installer and manufacturer warranties expect proof of regular servicing, so missed services can count against a warranty claim.
You pay in comfort as well. A neglected unit cools unevenly, takes less moisture out of the air and can push odours around the room. At work that affects how people feel and get on with things. In a bedroom it affects your sleep.
A maintenance agreement puts servicing on a schedule. Businesses use them, and so do homeowners who'd rather not have to remember. UK Aircon offers maintenance agreements covering residential and commercial systems, and our technicians service air conditioners from any manufacturer. Systems we install also come with a 5-year warranty that includes complimentary maintenance check-ups and discounted spares.
Clean the filters every few weeks when the unit is in heavy use and at least monthly during summer. In dusty environments, kitchens or homes with pets, they may need cleaning more often.
Most domestic systems need a professional service once a year. Commercial systems and those running long hours are commonly serviced every six months, and heavily used sites such as restaurants or server rooms often quarterly.
Systems containing refrigerant at or above 5 tonnes of CO2-equivalent must be leak checked at set intervals by an F-Gas qualified engineer, with records kept. Most single domestic splits fall below that threshold, but larger multi-split and VRF systems often do not.
A TM44 inspection is an energy assessment required at least every 5 years for air conditioning systems in a building with a combined cooling output over 12kW. It reviews system efficiency and controls and recommends improvements.
Owners can clean filters, wipe the casing and keep the outdoor unit clear. Coil cleaning, electrical checks and anything involving refrigerant should be done by a qualified engineer, and refrigerant work legally requires F-Gas certification.
For a one-off service or a maintenance agreement on a home or business system, see our air conditioning maintenance and repairs page, or contact UK Aircon for a free quote. We reply within 24 hours.
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