Pump for central heating system

Claim 1

In a central heating system including a boiler for heating liquid, heat transfer means for transferring heat from said liquid to the environment, and circulation means including pipe and a pump for circulating liquid through said pipe between said boiler and said heat transfer means, the improvement in said circulation means comprising: a pump including: (a) a housing adapted to be connected in series with said pipe, (b) an induction motor having unencapsulated motor windings and coaxially mounted within said housing, said induction motor having a casing which is unsealed to ensure that liquid enters said casing, said liquid contacting the motor windings for cooling said induction motor, said induction motor for rotating a peller within said housing to cause said liquid to flow an annular passage between said housing and said casing, and (c) a motor power supply associated with said induction motor for converting an available alternating current voltage having a given frequency into a modified multiphase alternating current voltage having a higher frequency to energize said induction motor so as to produce a given flow requirement of said central heating system, said modified voltage having an amplitude not exceeding 25 volts and having a frequency greater than 70 Hertz, whereby said induction motor cannot be energized directly by said available voltage at said given frequency to produce said required flow and must be energized by said modified voltage at said higher frequency to produce said required flow.