For most UK homes, the honest answer is once a year. A domestic split system doesn’t need fussing over every month, but it does need one proper visit from a qualified engineer annually — and there’s a warranty reason for that as well as a mechanical one, which we’ll come to. Between visits, there are a couple of small jobs you can safely do yourself that make a genuine difference.
Why annual, and when more often
An air conditioning unit is basically a fan, a heat exchanger and a sealed refrigerant circuit. Left alone, the filters clog with dust, the coils pick up a film of grime, and the condensate drain slowly furs up. None of this breaks the unit overnight — it just makes it work harder, cool less, and cost more to run. A yearly service resets all of that.
Once a year is right for typical use: cooling through the summer, perhaps some heating in spring and autumn. If you run yours hard year-round — remember a modern split is a reversible heat pump, so plenty of people heat with it all winter — twice a year is worth considering. The same goes if anyone in the house has allergies or asthma, or if you have pets whose hair ends up in everything, filters included.
What a proper service actually includes
A real service is more than a quick wipe and an invoice. A good engineer will typically:
- Remove and deep-clean the filters and the indoor unit’s coil, where mould and bacteria like to settle
- Clean the outdoor unit’s coil and check the fan and casing
- Flush and check the condensate drain, the most common cause of indoor units dripping water
- Check refrigerant pressures and inspect the pipework for any sign of a leak
- Tighten and test the electrical connections, then run the system in both cooling and heating and check the temperatures it’s actually delivering
If a visit takes ten minutes and nobody opens the unit up, you haven’t had a service. Anything involving the refrigerant circuit itself — topping up, repairing a leak — legally requires an F-Gas certified engineer, so it’s worth asking about certification before you book.
What it costs
As a rough guide, budget somewhere in the region of £60 to £120 for an annual service on a single split system — prices vary by area and by firm, so get a couple of quotes rather than taking any figure as gospel. Multi-splits cost more because each indoor unit needs doing, though most firms charge less per unit after the first. Some installers offer maintenance plans that bundle the annual visit with priority call-outs; whether that’s worth it depends on the price, so do the arithmetic rather than assuming.
Set against what a system costs to run, servicing usually pays for itself. Dirty filters and coils force the unit to work harder for the same result, and at today’s electricity prices a system running below its best quietly adds to the bill over a summer.
The warranty catch most people miss
Here’s the part that rarely makes it into the sales conversation. Manufacturer warranties on split systems — often five years or more on the established brands — are commonly conditional on the system being serviced annually by a qualified engineer, with records kept. Skip a year and a warranty claim can be refused, even on a fault that had nothing to do with servicing. Check the terms on your own unit rather than assuming.
That means the real cost of owning air conditioning isn’t just the installed price — it’s the installed price plus an annual service for as long as you want the warranty to hold. Nobody mentions this at quote stage, so factor it in yourself: over a long warranty it adds up to several hundred pounds of near-obligatory maintenance. Still usually worth it — it’s just better to know before you buy than to find out at claim time.
What you can safely do yourself
Between services, there’s a short list of jobs any homeowner can do — and they’re genuinely worth doing:
| Job | How often | Who |
|---|---|---|
| Clean or vacuum the dust filters | Every few weeks in heavy use | You |
| Clear leaves and debris around the outdoor unit | Each season | You |
| Deep-clean coils and flush the drain | Annually | Engineer |
| Check refrigerant pressures and leaks | Annually | F-Gas engineer |
| Electrical checks and full test run | Annually | Engineer |
The filters are the big one. On most indoor units, the front panel lifts up and the mesh filters slide out. Vacuum them or rinse them in lukewarm water, let them dry fully, and slide them back. Five minutes, no tools, and it keeps airflow — and efficiency — where it should be. While you’re at it, make sure nothing has grown up around the outdoor unit; it needs clear space to breathe.
What you shouldn’t do is anything beyond that. Don’t open casings, don’t spray cleaning products into the coil, and never touch anything on the refrigerant side — handling refrigerant without F-Gas certification is against the law, and for good reason.
Servicing or repair?
A service is preventative. If your system is already misbehaving — weak or warm airflow, ice on the pipes, water dripping indoors, a musty smell, or error codes — that’s a repair visit, not a service, and it’s worth booking sooner rather than later. Small faults caught early tend to stay small.
Finding someone good
Any F-Gas certified engineer can service a split system — it doesn’t have to be the firm that installed it, though using the installer keeps warranty paperwork simple. If you’d rather not vet firms yourself, Coolhouse matches you with one vetted local engineer rather than selling your details to five — tell us about your system and we’ll put you in touch.