Check the requested mode
Confirm that the controller shows heating mode and choose a temperature above the current room temperature. Some systems delay the indoor fan while the coil warms, so allow the response time described in the manufacturer manual.
Make sure doors and windows are closed and accessible filters are not restricted. If several indoor units share one outdoor unit, check whether the connected system permits different operating modes at the same time.
Understand defrost and operating limits
During heating, an outdoor unit may periodically defrost. Indoor heating can pause and the outdoor unit may release water or vapour; this can be normal. The exact sequence and operating limits depend on the model.
A continuous failure to heat may involve airflow, sensors, controls, outdoor-unit operation, refrigerant condition or system sizing. Published performance data and measured operation are needed before drawing a conclusion.
Arrange diagnosis when heat does not return
Do not open covers or attempt electrical or refrigerant work. Switch the system off if there is a burning smell, repeated tripping, abnormal noise or visible damage. Otherwise, note displayed codes and how long the problem continues.
Top Local can check reversible air-conditioning systems across Kent. Share the indoor and outdoor model details, outside conditions, controller setting and whether other connected rooms are working.