When your air conditioning stops cooling properly, it's frustrating — but the cause is very often something simple. Here are seven of the most common faults we see, and which of them you can sensibly check yourself before booking an engineer.

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1. Dirty Filters

By far the most common culprit. Clogged filters choke airflow and cripple cooling performance. Most filters simply clip out and can be rinsed clean under a tap — worth doing every few weeks through summer, especially if you have pets.

2. Blocked Outdoor Unit

Leaves, grass cuttings and general debris around the outdoor condenser stop it shedding heat properly. Keep at least 30cm clear on all sides of the unit, and check it after any heavy wind or garden work nearby.

3. Incorrect Thermostat or Mode

It sounds obvious, but it's a genuinely common cause of a "broken" system that isn't broken at all. Units left in "fan" or "dry" mode won't cool the room. Check the remote is actually set to cooling mode, and that the target temperature is set below the current room temperature.

4. Low Refrigerant or a Slow Leak

If the system runs constantly but barely cools, you may have a refrigerant leak. This needs an F-Gas certified engineer — topping up refrigerant without first finding and fixing the leak is both illegal and pointless, since it will simply leak out again.

5. Frozen Coil

Ice forming on the indoor unit usually points to restricted airflow or low refrigerant. Switch the system off and let it defrost fully before doing anything else, and check the filters once it has — that alone resolves a surprising number of frozen-coil call-outs.

6. Blocked Condensate Drain

A blocked drain can trigger a safety cut-out, stopping the unit running altogether, or cause water to drip indoors from the indoor unit. This is a common and often overlooked cause of a system that simply refuses to run.

7. Electrical or Sensor Faults

Tripped breakers, failed capacitors or faulty temperature sensors can all stop a unit cooling, and none of these are safe or sensible to investigate yourself. These need professional diagnosis. If the simple checks above haven't restored cooling, a quick local call-out will pinpoint the actual fault before it gets worse — or more expensive.

Simple checks not fixed it?

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