Can I use heat gun to remove wall paint?

If you have paint peeling/flaking off the wall, it might be a better option to scraping off loose paint and put on a skim coat of plaster/joint compound. I've used a heat gun to remove large areas of paint and its not fun. If you're determined to do it, be wary of holding the heat gun in one spot too long. Try and warm up 1 foot diameter area and then use as wide a putty knife as you can to scrape while heating up the wall in front of the knife edge.

You should be aware that if the paint has lead in it, a heat gun can vaporize it, which is as dangerous as any citrus strippers might be.

I would also take some time to figure out why its flaking in that area under the window. Is it from a leak around the window? Maybe the frame outside is not sealed or the caulk has dried up and cracked. It would be annoying to fix the wall, paint it and then have it reoccur a few months later.

I have done this on multiple layers of old oil and latex paint.

The heat gun does work. If you are lucky, you'll soften a lower layer of paint and be able to lift off sheets with a scraper.

If you are unlucky, you'll burn the paint, creating nasty little blisters that have to be scraped and sanded carefully, and you'll burn yourself with the heat gun.

Fumes can be nasty, and the process is time consuming. But it won't raise the grain the way that chemical strippers do.

Buy an assortment of metal scrapers before starting -- nooks and crannies can be tough to get into.

Citrus based paint strippers work very well, and they smell like citrus.

When stripping paint, sometimes it is required to do it in stages, apply stripper, scrape and repeat (maybe several times).

On paint that is very difficult to remove sometimes using a heat gun will help soften the paint so it can be removed. Sometimes you need to employ both methods to achieve effective results.

I would use the citrus stripper and see how it goes.

Can I use a heat gun on my kitchen wall?

If, as you guess, the wall is plaster over brick then a heat gun used carefully will not damage the wall. If it is drywall (Sheetrock) then you need to be very careful. Drywall is gypsum sandwiched between two layers of paper so once you have removed most of the paint you could scorch the paper if not careful.