“Few months ago I dropped robo and it was dented.”
If there’s a gap in the bottom of the malt pipe and mesh screens, that’s not good. If grain is getting through, it may be the cause of the scorching. Have you done many brews in the robo? Was this one any different - e.g. more grain than usual ? Did you get any overflow down the centre pipe? - Could you get a piece of silicone tubing and split it length ways to fill the gap?
I’m guessing you’re in the US so 110VAC? My results may be different as we’re on 240VAC.
I mostly set my mash in temp at 78C with both elements on and wait for it to come up to temp. By the time I’ve finished dough in, I’ll set it back to 68C (I find the indicated temp is about 2 deg C higher than measured with a thermometer). I’ll still leave both elements on during the re-circulation - I run that generally for an hour, maybe 90 minutes … The thermostat will keep the temperature pretty close to what I want.
For the boil, I set the robo temp at 105C, both elements on and let it go nuts for an hour (lid off). I may get a little staining on the base where the elements are but that wipes off pretty easily at cleanup…
Apologies for talking Celsius … but you get my drift.
[Edit] forgot to say my RB is a 35L / 5 gal …
Hope this helps.