Dry running, also referred to as inadequate lubrication, occurs when there is air in the rotor chamber, meaning that rotating parts are not cooled and lubricated as they should be. Dry running leads very rapidly to destruction of the pump.
Reasons may include inadequate ventilation of the pump. In the event of installation at the highest point of the heating system, incorrect pre-pressure in the expansion vessel may cause air to enter. Vapour formation in the pump due to excessive temperatures.