Rebuilding the inner brick of my wood boiler?

For some reason the photo would not load for me, try posting a thumb directly to forum..depending on the size of the firebox and the way the wall refractory is attached, you will either remove and replace or veneer over the existing. Rutland has firebrick that is only about 1-1/2" thick , some high heat cement and you can veneer the firebox with new brick...

I can't see pictures either.

If the boiler sat unused for a long time, the refractory & mortar might have taken on moisture - than having real hot fires all of a sudden might have induced some damage. Better in that case to have a couple or few real small ones to get the moisture out first.

Also if that boiler has the pressure relief valve outlet routed into the firebox, that could also make for a very wet firebox if the previous owner ran the pressure up (waterlogged expansion tank?) or the relief valve was leaky. Which wouldn't be good for mortar.

Did the bricks themselves break, or did the mortar/cement deteriorate? Thinking that it has ordinary firebrick in there, so you should be able to get it fix up. Would just have to make sure you get the right stuff.

For laughs I tried this, and it worked:
https://www.dropbox.com/s/v8e9f9qmt8l0k95/20151208_010739.jpg

It doesnt look too bad, maybe some different camera angles.

IMO looking at your bricks they still look like they are in good condition , if they become loose at the cracks and start falling out then it is time to do some thing .