A rolling element bearing induction heater comprising: - a ferromagnetic core with first (11, 21), second (12, 22), third (13, 23) and fourth arms (14, 24) which complete a magnetic circuit of the core, whereby one of the arms is moveable so as to allow the rolling element bearing to be arranged for heating such that one arm of the core passes through its internal diameter; - at least first and second induction coils (7, 8, 31, 32, 33, 34); and - a heating cycle control circuit adapted to control the induction coils, characterised in that the control circuit comprises an inner ring temperature signal input and an outer ring temperature signal input, whereby the control circuit is adapted to control at least a portion of the heating cycle based on a difference between the inner ring temperature signal input and the outer ring temperature signal input, and is further adapted to: (i) apply a first power combination to the induction coils (7, 8, 31, 32, 33, 34) in a first portion of the heating cycle, to rapidly raise the temperature of an inner ring of the bearing (2, 52); and (ii) apply a second power combination to the induction coils in a second portion of the heating cycle, to raise the temperature of the inner ring of the rolling bearing at a rate lower than that during the first portion of the heating cycle, whereby a switchover between the first portion of the heating cycle and the second portion of the heating cycle is triggered by the difference between the inner ring temperature signal input and the outer ring temperature signal input. - a ferromagnetic core with first (11, 21), second (12, 22), third (13, 23) and fourth arms (14, 24) which complete a magnetic circuit of the core, whereby one of the arms is moveable so as to allow the rolling element bearing to be arranged for heating such that one arm of the core passes through its internal diameter; - at least first and second induction coils (7, 8, 31, 32, 33, 34); and - a heating cycle control circuit adapted to control the induction coils, characterised in that the control circuit comprises an inner ring temperature signal input and an outer ring temperature signal input, whereby the control circuit is adapted to control at least a portion of the heating cycle based on a difference between the inner ring temperature signal input and the outer ring temperature signal input, and is further adapted to: (i) apply a first power combination to the induction coils (7, 8, 31, 32, 33, 34) in a first portion of the heating cycle, to rapidly raise the temperature of an inner ring of the bearing (2, 52); and (ii) apply a second power combination to the induction coils in a second portion of the heating cycle, to raise the temperature of the inner ring of the rolling bearing at a rate lower than that during the first portion of the heating cycle, whereby a switchover between the first portion of the heating cycle and the second portion of the heating cycle is triggered by the difference between the inner ring temperature signal input and the outer ring temperature signal input. (i) apply a first power combination to the induction coils (7, 8, 31, 32, 33, 34) in a first portion of the heating cycle, to rapidly raise the temperature of an inner ring of the bearing (2, 52); and (ii) apply a second power combination to the induction coils in a second portion of the heating cycle, to raise the temperature of the inner ring of the rolling bearing at a rate lower than that during the first portion of the heating cycle, whereby a switchover between the first portion of the heating cycle and the second portion of the heating cycle is triggered by the difference between the inner ring temperature signal input and the outer ring temperature signal input.