First: know when to stop
If there is an indoor water leak, burning smell, smoke, electrical tripping or severe unusual noise, stop using the system. Switch off the dedicated supply only if safe, and seek professional help. Do not keep resetting a breaker. If there is a fire, leave the area and call 999.
Check the controls
Check the selected mode, target temperature, timer and remote batteries. In cooling, the target should be below room temperature; in heating, above it. Allow the normal start-up time described in your manual. Units on many domestic multi-splits need compatible heating or cooling modes.
Look at airflow
From a safe position, check that curtains or stored items are not blocking indoor airflow. Check user-accessible filters only as the manual allows, switching off as instructed before cleaning. Do not climb to inaccessible units or remove service covers.
What about a rattle or restart?
Note when the sound occurs and record it if safe. Do not press on a running unit, force a fascia or reach through a grille. Before any restart, record warning codes. Follow only the reset procedure for your exact model or our advice; a reset is not a repair.
Help us prepare
Send the affected room, model, mode, symptoms, when the issue started, and a photo of any fault code. We do not currently offer urgent breakdown call-outs; contact us to confirm availability.