There is never a convenient time for your air conditioning to break down. It always seems to happen on the hottest day of the year, when the house already feels stuffy and every room is a few degrees warmer than it should be. Whether your unit has stopped completely or is simply not performing as it should, an air conditioning problem can move from minor annoyance to urgent issue very quickly.
The good news is that not every fault needs an engineer. Some issues have simple fixes you can carry out yourself in a few minutes, while others genuinely need a qualified professional. This guide walks through what to check first, the warning signs that mean you should stop and call for help, what a repair is likely to cost, and how to stop the same thing happening again next summer.
Check the simple things first
It sounds obvious, but not every air conditioning issue is a major fault. Sometimes the fix is surprisingly simple. Before you assume the worst, work through these checks:
- The thermostat. Has it been switched off, or set to heating instead of cooling? Has someone changed the target temperature without realising? This is the single most common cause of a unit that appears to have stopped working.
- The power supply. Check your fuse box or breaker panel. A tripped breaker is easy to miss, and a simple reset can bring a system back to life.
- The air filter. A clogged filter restricts airflow and can cause a system to shut down or perform poorly. If the filter looks dirty, replace it. Filters are cheap, and running the unit with a clean filter avoids a lot of strain on the system.
These are quick checks, but they solve more problems than you might think.
Signs you need a professional
Not every issue needs immediate attention, but some do. You will want to act quickly if you notice:
- Warm air blowing instead of cool air
- No airflow at all from the indoor unit
- Strange noises, such as grinding, banging or buzzing
- Burning or unusual smells
- Water leaks or ice forming on the unit
TIP: If your system is making loud or unusual noises, or there is a burning smell, turn it off straight away. Continuing to run the unit could make the problem worse, and in some cases it creates a genuine safety risk.
Common causes of air conditioning failure
Air conditioning systems rarely fail out of the blue. There are usually small warning signs that, if caught early, let you prevent a bigger problem. The most common causes of failure include:
- Dirty or blocked filters. Restricted airflow makes the system work harder, which overheats components and reduces cooling performance.
- Low refrigerant levels. A slow leak means the system cannot transfer heat properly, so it blows warm air or runs constantly without cooling.
- Electrical faults. Capacitors, contactors and wiring issues can stop the unit starting, or cause it to cycle on and off.
- Frozen coils. Usually caused by restricted airflow or low refrigerant, ice on the coils blocks the cooling process entirely.
- Wear and tear. Fans, motors and compressors eventually fail, particularly on older units.
Regular maintenance picks up most of these issues before they become faults. But if you do find yourself with a faulty unit, it is useful to know what to do next, and when to call in an air conditioning specialist.
Why refrigerant work needs a certified engineer
If your system is low on refrigerant, you might be tempted to buy a top-up can and do it yourself. Do not. Refrigerant handling is regulated, and the rules are strict.
Under UK law, you must hold a recognised qualification to work on equipment containing fluorinated gas (F gas). The Environment Agency is clear: it is against the law to work with F gas without the correct certification, and you could face a civil penalty for breaking the rules. Refrigerant work on air conditioning and heat pump systems requires an engineer with a category 1 to 4 certificate, depending on the job. Leak checks, recovery, servicing and installation all count as regulated activities.
The practical consequence is simple: topping up refrigerant, repairing a leak or disposing of an old unit are jobs for a certified air conditioning engineer. A professional will also find and fix the leak rather than simply recharging the system, which is the difference between a lasting repair and one that fails again in a few weeks.
Repair or replace?
If your system is more than ten years old and the repair bill is heading towards half the cost of a new unit, replacement is often the smarter call. Modern units are significantly more efficient, which means lower running costs and better cooling, and they use refrigerants with a far lower environmental impact. An engineer can give you a like-for-like quote for repair versus replacement, and most will be honest about which one represents better value for your situation.
If the unit is newer, or the fault is a simple one like a failed thermostat or a clogged drain, repairing is almost always the right choice.
How to avoid a breakdown
A little maintenance goes a long way. The steps below will not guarantee your system never fails, but they will catch most problems before they become expensive:
- Book an annual service. A yearly check by a qualified engineer costs around £80 to £150 and is the single best way to catch small issues early.
- Clean or replace filters regularly. Every few months during heavy use is a good rule of thumb.
- Keep the outdoor unit clear. Remove leaves, debris and anything blocking airflow around the condenser.
- Do not block indoor airflow. Keep vents and the indoor unit free of furniture, curtains and clutter.
- Fix small problems promptly. A dripping condensate line or a slightly odd noise rarely fixes itself. Deal with it early and it stays a small job.
Find a trusted air conditioning specialist
When you need an engineer, it pays to choose carefully. Refrigerant work is regulated, so check that the company holds the right F Gas certification, and look for one that offers a warranty on both parts and labour. Reading recent customer reviews is the fastest way to separate a company that does careful work from one that does not.
You can search our vetted and reviewed air conditioning services to find a specialist near you, or browse our air conditioning specialists for property. Every trader on TrustATrader has been checked and comes with real customer reviews, so you can compare local engineers with confidence.
If your unit is old and you are weighing up whether to repair or replace, our guide on whether air conditioners are worth it in the UK covers the running costs and benefits in detail. And for the days before a repair is booked, our heatwave cooling tips will help you keep the house comfortable in the meantime.