We've got one in our kitchen and it looks lovely. It's got an oven and 2 hot plates ... not with lids like an aga, just hot plates so not child friendly at all. Anyway, we've lit it a few times and to begin with it heated the oven really well and we were able to use the hot plates too, but it seems to be not working as well. It is really old and I think it needs renovating but have no clue who would do this kind of thing. Anyone ever done anything similar, ever?!
I wonder if the chimney just needs sweeping so you get a good draw on it. Has it got a damper? If so, is it working properly (ie. not stuck shut)? It's worth looking at these basic things before getting the professionals in. You could always go to a wood burning stove/fireplace stockist and pump them for a bit of information.