starter 43 and the three phase winding of motor 23 during normal operation the contacts are closed thereby permitting cycling of the motor and thus the hydraulic pump by opening and closing the starter 43 upon detecting an overheated condition in the hydraulic fluid however the motor circuit between the starter and the motor is broken thereby preventing further agitation of the hydraulic fluid by the pump it should be noted that by breaking the electrical connection to the motor on the motor side of the starter continuous operation of the pump is avoided in case the starter becomes jammed or locked in a closed position furthermore in this arrangement power from the main supply to the computer will not be interrupted when the pump is shut down whereby the computer will be available to carry out certain down duty cycles after the pump is shut down as is conventional in most hydraulically operated lift systems a heater 80 is herein provided to maintain the temperature and thus the viscosity of the hydraulic fluid at a constant temperature the heater is immersed within the fluid contained in reservoir 11 and is connected to power supply 45 through normally closed contacts 54 in case of an overheat shut down contacts 54 are immediately opened to prevent further operation of the heater the possibility of the heater driving the already overheated fluid beyond its critical point is thereby avoided similarly in the event that.