Air conditioning maintenance: a UK home upkeep guide

Most air conditioning maintenance is a job you can do yourself. Cleaning or replacing the filters, wiping down the indoor unit, keeping the outdoor unit clear of leaves and debris, and checking the drain runs freely will keep a home system cooling well and running cheaply. On top of that, book one professional service a year. The one hard rule: anything that touches the refrigerant inside the unit, such as leak checks, top-ups or a "re-gas", must by law be done by an F-Gas registered engineer, never as DIY.

This guide covers the upkeep you can safely do between services on a wall-mounted split, a multi-split or a portable: what to clean, how to clean it, and how often. It also draws a clear line between the jobs that are yours and the jobs that are an engineer's, so you keep your unit efficient without doing anything unsafe or illegal.

Your air conditioning maintenance schedule

The simplest way to look after a unit is to work to a rhythm. This is the owner side of the job. The annual entry is the professional service, which is a separate booking.

Reverse-cycle units (the ones that heat as well as cool) are used all year, so keep cleaning the filters through the heating season too, not just in summer.

What you can do yourself, and what needs an engineer

The dividing line is refrigerant. Every safe DIY job stays away from the sealed refrigerant circuit and the electrics. Every job that opens that circuit is engineer-only, because handling fluorinated refrigerant such as R32 requires F-Gas certification by law, and doing it yourself on a split system is a criminal offence.

A sealed split should never need a routine "re-gas". If it is low on refrigerant, it has a leak, and that is a job for a certified engineer, not an annual chore.

One useful point on cost: a correctly installed system does not lose refrigerant. The "annual re-gas" idea comes from car air conditioning and does not apply to a home split. Portable units are different again: they are sealed and pre-charged at the factory, so there is no refrigerant work for you or an engineer in normal use.

How to clean an air conditioner filter

The filters are the single most important thing you can look after, and cleaning them takes a few minutes. A blocked filter chokes the airflow, so the unit works harder, cools less and costs more to run.

1. Switch the unit off and isolate the power. Most splits have an isolator switch on or near the outdoor unit; turn it off before you start.

2. Open the front panel. On a wall unit it lifts up until it clicks; on a portable the filter usually slides out from the back or side.

3. Remove the filters. These are the flat mesh screens behind the panel. Note which way round they sit.

4. Clear the dust. Vacuum off light dust with a soft brush attachment. For a dirtier filter, wash it in lukewarm water with a little mild detergent and rinse it clean.

5. Dry it fully. Let the filter dry completely, in the shade rather than direct sun. Never refit a damp filter, as trapped moisture breeds mould inside the unit.

6. Refit and close up. Slide the filters back the right way round, close the panel and restore power.

Manufacturers suggest cleaning the filter often. Daikin and Mitsubishi Electric recommend roughly every two weeks in peak use, while LG UK suggests every one to three months. A practical UK routine is to check monthly through the cooling season and give the filters a proper clean every one to two months, more often during a heatwave or if you have pets or hay fever. Some units also have a finer air-cleaning or deodorising filter that is replaced rather than washed, typically once a year.

Cleaning the indoor unit

Beyond the filters, keeping the indoor unit clean helps airflow and keeps smells at bay. With the power off, wipe the casing with a soft, damp cloth and vacuum dust from the vents and louvres. Do not spray water into the unit or poke anything into the electrics.

The coils and fins behind the filters are a different matter. Cleaning them properly means opening up the unit, which exposes sharp edges and electrical parts, so that deep clean is part of the annual professional service. A few models come with a manufacturer "quick clean" brush kit for lightly dusting the visible fins with the power isolated; if yours does, follow its instructions and keep it gentle. Otherwise, leave the coils to your engineer.

Keeping the outdoor unit clear

The outdoor unit needs air to move through it freely. Once a season, and after autumn leaf-fall, clear away leaves, grass clippings and any debris on top of and around it. Cut back plants, and keep bins, fences and stored items far enough away that air can circulate. Make sure nothing is blocking the fan.

This is a safe job as long as you only clear around the unit. Do not open the casing, unbolt panels or touch the pipework and the insulated refrigerant lines running into the house.

Checking the condensate drain

When the unit cools, it pulls moisture out of the air, and that water drains away through a pipe, usually to outside. Keep the outside end of that drain pipe clear of dirt, leaves and insects so the water runs away freely.

The classic sign of a blocked drain is water dripping from the indoor unit or a damp patch appearing on the wall below it. Clearing the visible outlet is a DIY job; if water is still backing up, the internal drip tray or a condensate pump may need attention, and that is a service-visit task rather than something to dismantle yourself.

Cleaning and maintaining a portable air conditioner

Portables need the same filter care plus a couple of extras, because they collect their own condensate and get moved around.

• Filter: clean it about every two weeks in heavy use. Vacuum or rinse it in lukewarm water and let it dry fully before refitting, just as with a split.

• Casing and vents: wipe with a damp microfibre cloth, keeping moisture away from the vents.

• Water tank: drain any collected water through the drain plug at the base. Many modern portables mostly evaporate their condensate away through the exhaust, but check. Wiping the tank with a mild vinegar solution keeps bacteria and mould down.

• Exhaust hose: detach it now and then, clear any dust or mould, and make sure it is dry before refitting.

• End of season: drain the unit fully, clean and dry it, take the filter out and clean it, then store it covered in a dry place ready for next summer.

If you are shopping for a unit that is easy to live with, our guide to portable air conditioners covers the models and their upkeep.

Seasonal start-up and shut-down checks

A few minutes at each end of the season saves a call-out later.

Before the cooling season, clean the filters, clear the outdoor unit, check the drain runs freely, and run the unit on cooling for ten minutes to confirm it blows cold, drains properly and makes no new rattles or smells. Sort out anything odd before the first heatwave, when engineers are busiest.

At the end of the cooling season, clean the filters again. If you have a portable, drain it, dry it and store it covered. If you have a reverse-cycle split you use for heating, there is no shut-down: just keep cleaning the filters through the winter.

Why maintenance matters for your bills

Clean upkeep is not just tidiness, it is money. A clogged filter restricts airflow, so the unit runs longer and draws more power for the same cooling. The US Department of Energy estimated that swapping a dirty, clogged filter for a clean one can cut an air conditioner's energy use by 5% to 15%, and UK manufacturers make the same point: a dirty filter means higher bills.

Here is what that looks like in practice. Say a wall split draws about 0.8kW of electricity and runs 8 hours a day. That is 0.8 × 8 = 6.4kWh a day. At the Ofgem price cap of 26.11p/kWh, that is 6.4 × 26.11p = 167p, or about £1.67 a day to run. A neglected filter adding 5% to 15% to that wastes roughly 8p to 25p a day, which is around £2.50 to £7.50 over a month of similar use, for a clean that costs nothing. Kept clean, a system also runs quieter, breaks down less and is more likely to reach a typical 10 to 15 year life.

Running cost is illustrative and uses the Ofgem price cap of 26.11p/kWh, correct as of August 2026. The cap changes quarterly (the next one is around 26 August 2026), and from 1 October 2026 VAT on domestic electricity is cut from 5% to 0%, which will trim these figures slightly. Real power use varies by unit and settings, so check current rates before budgeting.

For the fuller picture on bills, see our guide to whether air conditioners are expensive to run.

When to call a professional

DIY upkeep keeps a unit ticking over, but it is not a substitute for the annual service, where an engineer checks the refrigerant and pressures, deep-cleans the coils, tests the electrics and looks for leaks. Many manufacturers also want to see that a system has been serviced to keep the warranty valid.

Call an F-Gas engineer sooner if the unit is not cooling despite clean filters, if it leaks water you cannot trace to the drain outlet, if you smell burning or hear grinding, or if it needs refrigerant. For how often to book and what a service includes, read our guide to air conditioning servicing, and if the unit has stopped cooling properly, our guide to why an air conditioner is not cooling walks through the checks.