The duration of Legionella inspection varies depending on the size of the property and it's water systems.
Your assessor will need time to take a digital temperature reading of every hot and cold tap, as well as conducting visual inspections of all taps and showerheads. This including exterior taps and outdoor houses.
For example, a one-bed flat with one bathroom and a combi boiler could take 20 minutes, whereas a three-bed house with two bathrooms and a water tank could take an hour.