I had some luck using my steamer-with high pressure steam on it, but not a lot of luck. You might contact a professional clean up place-they deal with soot removal and they might have some tips.

Hi,
I actually saw an hgtv show where the host used scrubbing bubbles and a scrub brush on dirty brick. Never tried it, but it might be worth a shot. Good luck.

I saw that same HGTV show with Sabrina Soto cleaning the fireplace. It was amazing! I can't find the show but here's another reference to that episode.

Here is a link that might be useful: cleaning fireplace brick ala get it sold

I cleaned my in-laws' fireplace hearth of years of soot with Charlie's Soap liquid spray. Sprayed it on, let it sit a few minutes and rinsed. It all came off beautifully. I had tried the usual attempts at cleaning and using a steamer with no luck.

Old House Journal just had an article on a product that you paint onto the brick, let dry (it becomes a thin membrane, maybe something like rubber cement), then pull off again ... supposedly all the soot comes with it. I'll see if I can find the name of the product.

Thanks, all. I did have scrubbing bubbles in the house, so I started with those. So far, it doesn't look great but I really need to wait and see how it looks when it dries....

Oven cleaner and water with dishwashing soap to rinse off. It is really easy and does the job. Although messy and wear gloves.

I had great success with Quick N Brite.

One of those "As Seen On TV" things that actually worked.

Here is a link that might be useful: http://www.amazon.com/Quick-N-Brite-Biodegradable-Co/dp/B001F893OA