A temperature cycling system (10, 110) is provided for repeatedly heating and cooling a reaction mixture (16). The system (10, 110) includes a first heater (27) and a second heater (28) each movable between a first orientation in which the first or second heater (27, 28) affects the temperature of the reaction mixture (16) and a second orientation in which the first or second heater (27, 28) does not substantially affect the temperature of the reaction mixture (16). During temperature cycling, the second heater (28) is in the second orientation when the first heater (27) is in the first orientation, and the second heater (28) is in the first orientation when the first heater (27) is in the second orientation.