I recently purchased the "better" Harbor Freight heat gun and I like it. I needed a new heat gun for studio and I decided on this model solely because it comes with a screw-on base that allows you to use it hands-free.
You got lucky you were there to observe and stop before any other issues could happen. A friend told me a horror story of a kiln that never shut off -- he fired a load in his outdoor carport kiln area and then had to leave home for a long time and trusted his equipment to do its thing like it "should". Came home at night when the kiln should have been off hours before, but saw glowing coming from underneath.....kiln sitter got stuck and the timer also failed somehow allowing the kiln to keep firing - melted all his glaze off the pots enough to eat through the floor of the kiln, hence seeing glowing from underneath!
$100 for what "guts" parts on the Brent wheel pedal? there are several parts inside the foot pedal, the entire assembly is around $150. I've personally only seen one item actually fail inside a Brent foot pedal, the plastic lever arm, and for that part it was only like $6. Even if it was the speed controller, the most expensive part on the assembly, it's only around $65.
Like said, check the fuse - it should be located on the back side of the power switch box where the power lead and foot pedal lead enter/exit. Standard glass fuse, if you see a break in the wire inside it's no good.
My guess is that you have an issue inside the foot pedal - if you said you plugged it in and it spun erradically, then you shut it off and it won't work anymore....usually when I see that it means the speed controller inside is still engaged slightly enough to make the wheel spin, but if you couldn't change the speed then the fork inside the pedal is not engaging the lever properly. Inside the pedal is a plastic "fork" that moves the speed control lever switch up/down -- what happens sometimes is the fork gets loose and slides around (it's adjustable with a set-screw) and the fork prongs no longer engage the switch anymore...or the fork prong breaks..like if you accidentally drop the pedal on the floor or stomp on it too hard/fast. My advice is to open up the foot pedal and see if anything inside looks out of ordinary, I bet it's something simple.
We use an iron mix similar to the 1st suggestion, only ours has some clay added in there. It's not equal parts like an underglaze, it's more like 3 parts Iron, 2 parts flux (Gerstley borate) and 1 part clay (EPK) for suspension. Use CMC gum solution instead of plain water. Adding manganese dioxide will make it more black vs iron red