Is it one fixture or the whole home?
If only one tap has a problem, mention that when you call; the water heater may not be the source. If every fixture has lost hot water, note when it started and whether the household had unusually heavy use beforehand. A storage tank running out after several showers is a different symptom from a complete loss of heating.
Identify the equipment safely
Record whether you have a tank, tankless unit or heat pump water heater, along with its model number if accessible. Note any display message that can be read without opening panels. Report visible leakage, unusual sounds or a recent utility interruption. Do not relight burners, change gas settings, remove electrical covers or repeatedly clear a fault.
Arrange the right help
Call to discuss the symptoms and available appointment options. Water near electrical equipment, gas odour, a CO alarm or smoke requires immediate safety attention rather than an ordinary booking. Stay clear of wet electrical equipment; for gas or CO concerns, leave and seek emergency help from outside. If replacement is being considered, our hot-water page explains the starting options; a site assessment determines the appropriate installation.