We started having an occasional smell of rottenness (we originally thought it was a guest with a gas problem) about a year ago. Then we realised it was not only stronger but more sewagey 7mths later but put it down to a rotting bird or rat caught in the chimney or under the floorboards. But as this house is rented we waited for some reason. Then it became rancid 6 weeks ago and we've been desperate ever since. We initially thought it was an open man-hole cover that was next to our front room and so had that cleaned and replaced back, then we thought it was blocked drain so we had that unblocked by a council specialist then we found out that there was a cap thingy missing off a sewage end pipe but that was replaced and capped THEN we made sure every hole was filled to stop this smell coming in from the outside but that didn't do anything because although now the room is air tight the smell is soooooooo bad we have had to vacate it and tape the door up because the smell is so distressing. We have a newborn baby and we have both been unwell since the birth and we are thinking that the smell must be coming from the floorboards!! The sewage man and a health authority man said that it was highly unlikely to be a cracked pipe flooding our foundations (and we don't have a basement). What is the smell? My landlord has promised to rip up the floorboards for us soon.

This is reminding me of the "mouse poison". What happened in that instance is that the mice were not caught, they went back into the walls carrying poison. Some mice died and rotted in the walls, others survived and brought in more poison.

Look for mouse droppings.

Somewhere on AMHD is that thread.

The sewage man and a health authority man said that it was highly unlikely to be a cracked pipe flooding our foundations (and we don't have a basement). What is the smell? My landlord has promised to rip up the floorboards for us soon.

There isn't a crawl space under the house?

Do you have any floor drains, or a sink that is not used that often? The water may have evaporated out of the U-bend. Try pouring a bucket of water down the drain.