Oversink units are supplied with an inlet valve that, when opened, allows the mains cold water supply to enter the heater and displace the hot water stored in the cylinder.

As the valve controls the displacement, the outlet is open to atmosphere so that when the unit heats up, the expanded water is allowed to drip from the spout into the basin. No other outlet should be used in conjunction with this type of product.

• Typically, they are supplied from the water mains although supply from a cistern can be used as long as there is a minimum head pressure of 3 metres.
• The 3kW element provides a fast recovery from cold.