When you told Andy M. what type of pots you are using I knew instantly why you needed a heat diffuser. I'm guessing your food is scourching in a spiral pattern that matches the coil on your burner? I grew up on Revereware ... that was always a problem - and the only solution seemed to be to use the "double boiler" insert that came with it for things like thick soups, stews, chili, etc.
There are 3 major heat diffusers/flame tamers ... Kuhn Rikon
(but they are specifically for gas burners), Nordic Ware
, also a flat disk like Kuhn Rikon, claims theirs will work on both gas or electric, and Ilsa
, which is patterened, (they don't specify cooktop but since they are made in Italy I would be inclined to think probably intended for gas but might also work on electric). But, there are still potential "hot-spot" problems with these ... just different. In the case of the Nordic Ware ... the hot-spot would be around the edge of the burner plate (8-inches), assuming the base of your pot is larger than 8-inches. With the Ilsa you could just be trading a "spiral" hot-spot for a "star burst" pattern.
The problem is that Stainless Steel is a really lousy heat conductor because it heats unevenly and the copper on the Revereware pots is just too thin to really do the job of evening out the heat distribution (which is why you are having problems). And, while reducing the heat a bit might help in some instances ... it's going to take more heat to keep a 16-20qt pot at a simmer than 4-6 qts, so that really isn't an option in your case.
IMHO - I think this is a case where you might want to get a new pot that is up to the task (thick stainless with an aluminum disk on the bottom) if you want the best results. Like Katie said - the aluminum disk is a built-in heat diffuser. Now, some people want to vilify encapsulated aluminum disk bottoms on SS cookware ... when you get into pots 12-qt and larger even All-Clad uses them, and so do the commercial cookware folks like Vollrath.
All-Clad has an outlet store
where they sell irregulars for big discounts - but the also sell some discounted first-quality items ... and the big pots
(12/16/20/24 qt) they sell are first quality (no defects). Here are the commercial SS Vollrath stock pots
from my favorite restaurant supply. The All-Cald pots come with the lid, pots and lids from a restaurant supply are sold "à la carte" - sold seperately.
FWIW - I got the All-Clad multi-cooker about 6 years ago (12-qt) and I've never had another a problem with scorching or burning when making a big pot of sauce/chili/soup on either my original gas stove, or the electric stove my apartments replaced them with about 5 years ago. I was so impressed the first time I used it I bought one for both of my sons and my daughter for Christmas presents ... and they don't have any more problems, either.
Hope I helped more than I confused you!