Switch

Sandtree

What heating and hot water source do you have in your property?

As others have said, based on whats written on it it would suggest that its a water heater. For example in our last rental it was on Economy 7 and all electric so the water was heated overnight in the tank on the cheaper electricity but could run out during the day if usage was higher than normal and so there was a switch to turn the top element on based on more expensive day time energy to heat it up. Similarly as a kid we had a gas boiler with a hot water tank but again there was an electric element you could turn on to top up the heat rather than firing up the boiler.

Obviously, the label on the switch could be misleading as ultimately its just a fused isolator and so could be for a heated towel rail, extractor fan, electric shower or pretty much anything.