What you may be thinking of a "flame weeder", usually a torch of some kind conected to a propane cylinder. Heat can help control many "weeds", if done correctly.

Here is a link that might be useful: Flame Weeding

Here is a link. I don't think it is a flame but radiant heat.
any thoughts on use for a home owner?
cherry

Here is a link that might be useful: Radiant heat for weed control

Although I have thought about using flame for weed control I have not tried yet.
I think it would not get to the bulb and bulblets of the buttercup.
Would you consider Round Up? That will kill down to the bulbs.

This is something that I would never use on a plant that could release oils when heated, like poison ivy. Lesser Celandine it might work but although I do not like RU it or another broad leaf herbicide may be your only choice.

That radiant heat thingy still uses flame. The only way you will get heat from it is with a flame although not one you usually think of.