Heating system with steam radiators

A building heating system with a plurality of steam radiators comprising:

• a steam boiler;
• a feeder conduit connecting said boiler to the radiators;
• a return conduit connecting the radiators to said boiler;
• a vacuum pump disposed in said return conduit for pumping condensed water from the radiators to said boiler;
• a vacuum pressure sensing means for generating a signal indicative of the actual vacuum in said return conduit at a location between said vacuum pump and the radiators;
• a temperature sensing means for generating a signal indicative of the actual temperature of the heat transfer medium in said return conduit;
• and
• a control unit, responsive to the signals from said vacuum sensing means and said temperature sensing means, for producing an output signal in dependence upon a mutual directly proportional relationship between the actual values of the vacuum and the temperature of the heat transfer medium in the return conduit for providing shut off of said vacuum pump when the mutual relationship between the actual values of the vacuum and the temperature of the heat transfer medium in said return conduit is such that there is a risk of steam occurring in said return conduit, and for also providing restarting of said vacuum pump when the risk has ceased.