We have a back boiler in our front room, the water pipes from it run up inside the chimney breast and then go under the bedroom floor (that the smell is in) and run to the water tank in the airing cupboard next to the room. I've lifted the floor boards in the bedroom and the smell seems to be coming from where the pipes go down to the boiler. I can see no leaks and the water level in the header tank hasn't dropped. The boiler has a flue that goes up the chimney breast and was serviced within the last 3 months. If i turn the heating off and just run the hot water the smell seems to subside markedly.
