The short answer
Call an engineer when simple checks don't fix a problem, and switch off straight away for burning smells, smoke, a circuit breaker that keeps tripping or signs of a refrigerant leak. Refrigerant, electrics and anything inside the casing are work for a qualified engineer.
On this page
An air conditioner brings together mains electricity, pressurised refrigerant in a sealed circuit, and water. Knowing what you can check yourself saves an unnecessary call-out, and knowing where to stop keeps you safe and protects the system.
Checks to make first
Most of these take a minute and need no tools.
- The remote. Fresh batteries, the right mode, a sensible temperature and no timer or sleep setting you'd forgotten about.
- Power. The isolator switch is on and the circuit breaker hasn't tripped. Reset a tripped breaker once at most.
- Filters. Clean them if they're dusty.
- The outdoor unit. Nothing blocking it, such as leaves, snow or stored items.
- Heating on a cold day. Wait a few minutes in case the unit is defrosting.
- Multi-splits. Every room is set to the same mode, heating or cooling.
- Error codes. Note the code and look it up, as described in error codes and flashing lights.
Not cooling or heating properly goes through these checks in more detail.
How urgent it is
| Situation | Urgency | First step |
|---|---|---|
| Burning smell, smoke or sparks | Now | Switch off; call 999 if there's fire |
| Circuit breaker keeps tripping | Now | Leave it off and call |
| Buzzing or crackling from the unit | Now | Switch off and call |
| Water near sockets or wiring | Now | Switch off at the isolator and call |
| Hissing with oily marks on pipes | Now | Switch off, open windows, call |
| Unit or bracket damaged or loose | Now | Switch off, keep clear, call |
| Grinding, scraping or banging | Soon | Switch off and call |
| Not cooling or heating after checks | Soon | Note what you've checked |
| Error code that keeps returning | Soon | Note the code and model numbers |
| Water dripping indoors | Soon | Clean filters, check the drain outlet |
| Musty smell with clean filters | When convenient | Book a service |
| Yearly service due | When convenient | Book before the busy season |
For anything marked "now", switch the system off with the remote, and at its isolator switch or circuit breaker if you can reach it safely. Don't switch it back on until an engineer has checked it. If there's smoke or fire, get everyone out and call 999.
If you suspect a refrigerant leak, open the windows and keep naked flames away. R32, the refrigerant in many home systems, is mildly flammable, although a home system holds only a small amount.
What not to do yourself
- Don't open the casing of the indoor or outdoor unit, or remove anything beyond the front panel and filters.
- Don't touch the refrigerant pipes, valves or joints, or try to add refrigerant. Anyone working on refrigerant needs the right F-gas qualification, and refrigerant must never be released.
- Don't work on the wiring, the isolator or the circuit.
- Don't move the unit, bend the pipes or try to re-level it.
- Don't spray cleaners or chemicals into the unit.
- Don't keep resetting a breaker that trips or a code that keeps coming back.
Choosing who to call
Start with your installer, especially while the system is under warranty. Check the warranty terms before anyone else works on it, because some warranties set conditions on servicing and repairs.
If you use someone else, anyone who works on the refrigerant circuit needs the right F-gas qualification, and the business needs a company F-gas certificate. Ask about both. Why installation needs a certified engineer explains why they matter.
A fault in the electrical supply to the system, rather than in the unit itself, may need an electrician.
What to have ready
- The model numbers of the indoor and outdoor units, from the labels on each.
- The installation date, the warranty paperwork and any service records.
- The error code or flash pattern, and what the system was doing at the time.
- What you've already checked or tried.
- Photos, or a short video if the problem is a noise.
- How the engineer can reach the outdoor unit, especially if it's high on a wall and needs a ladder or access equipment.
For routine care between problems, what a service involves explains what a regular visit covers.
Related guides
- What a service involvesA service is a clean and check of the whole system, indoors and out, plus tests of how it runs and a look for leaks and wear. Manufacturers typically recommend one regularly, often once a year.
- Error codes and flashing lightsError codes and flashing lights usually show that the system has detected a problem, but they mean different things on different makes and models. Look the code up using your model number, and give it to the engineer if you need one.
- Not cooling or heating properlyStart with the simple causes: the mode and setting on the remote, timers, dirty filters, open windows and a blocked outdoor unit. If those are fine and it still struggles, it may have a fault or leak that needs an engineer.
- Why installation needs a certified engineerA split system is joined into a sealed refrigerant circuit on site, and in Great Britain anyone doing that work needs the right F-gas qualification, with the business holding a company F-gas certificate. Poor work can cause leaks, damage and safety problems.