Although it will probably be a very dirty job, replacing your old broken or damaged firebricks couldn't be easier. Each stove is different so we can only provide you with some general principles here. If you still have your stove handbook then always refer to this first, although in our experience not many of them are particularly helpful when it comes to firebrick removal.
Firstly, ensure that any porous surfaces like stone hearths and floor coverings are protected from soot and debris. Wear a protective face mask.
Take some time to work out exactly how the firebricks are held in place. On some stoves you may have to first lift out the baffle plate, which is inside the roof of the stove, to release the firebricks because this has been designed to rest on top of the bricks and help secure them. To remove the baffle, in most cases, it's simply a matter of pushing one side upwards whilst dropping the other side downwards and then moving the baffle plate outwards at angle from the fire chamber. It's advisable to clean the baffle and flueway before you attempt to remove it as it will probably be extremely dirty. Baffles can be very heavy so you'll probably also need to use two hands. Make a note of exactly the way that the baffle plate came out. This is because of their shape they can sometimes be confusing when it comes to putting them back in. On other stoves the firegrate may also have to be removed and on some the firebricks are simply held in place by merely being tightly fitted and placed in a particular order. If your baffle or firegrate are damaged or warped it maybe time to consider replacing them and you can find competitively priced replacements at www.stovespareparts.com
Once any baffle or firegrate has been removed you may then need to use an old kitchen knife or chisel to help prise out the damaged brick, being careful not to damage the neighbouring firebrick. As we've stated bricks may need to be removed in a particular order so that you can then get at the brick that needs replacing. You may find that the new firebrick needs some minor adjustments to its shape and size and this can be easily accomplished with gentle sanding or trimming with a sharp saw – only making minor adjustments at a time until you achieve a precise fit. What you don't want to do is to create is a new significant gap. If for some reason the replacement leaves firebrick leaves a gap between 2 to 5mm Always wear a protective face mask when undertaking sawing or sanding of vermiculite panels.
Your old refractory clay bricks can usually be recycled as 'hard core' at your local authority recycling centre. Vermiculite bricks are are not recyclable but can usually be safely placed with other non-recyclable material at your local authority recycling centre. Always ask your local authority for advice.