Compare with normal operation

Think about the system’s previous behaviour. Has comfort changed in every room, only under particular weather conditions or at particular times? A comparison with normal operation is more useful than a general impression that the system is weaker.

Look for supporting clues

Error codes, altered airflow, new noise or unexpected cycling can add helpful context. Do not assume that a single visible symptom identifies the cause; the aim is to give a complete picture for assessment.

Choose the right kind of visit

An annual service is useful for routine care. If the system has a sustained performance concern, unfamiliar behaviour or a controller message, diagnostics or breakdown support may be the more appropriate starting point.