IKA RET Basic safety control-visc hotplate/ stirrer digital probe to repair

used IKA RET Basic safety control-visc hotplate/ stirrer with temperature probe. digital display shows temperature. Hot/stirring plate diameter 5.5 inches. 115v. upon powers up. the unit heats up for several seconds then shows Er 4 message. that means "Difference between target and actual speed exceeds 300 rpm". looks like the stirring options does not work at all- for parts or repair- no return. no refund. lot con3/1