A digital stirring hotplate in decent used condition will set you back about $250. I paid a fraction of that for one with a broken heating function. The problem turned out to be nothing more than a duff switch.
In the past I have tried and failed to repair a hotplate with a knackered stirring motor. I reckoned it had to be easier to fix a stirrer with a broken heater. My guess was a burned out element or triac but everything looked shipshape inside. Maybe the thermocouple interface was bust?
It was dumber than that. The PCB behind the front panel was misaligned and one tactile switch couldn't be activated. And I am not a man to shrink from the challenge when faced with a screwdriver bodge job.
Now I won't be putting green food colouring in my yeast cultures, but it does make for a snazzy vortex.