Hi, no it's with the combustion chamber,I've been servicing my webastos for over ten years years,have you had a Webasto apart? If so I will describe it a little better if a can,as I've got rid of the porous chamber and reassembled the unit,no pics to show,if you withdraw the burner tube you can see in to the chamber which has fins down the side,at the bottom there are numerous little nodules,it has become porous in the Centre of those nodules,how I discovered it was when I switched the unit on I heard gurgling coming out of the exhaust, thought a boat had gone past and pushed water in the outlet, removed it drained the water it was fine hour later it started again!? Removed the Webasto stripped and checked noticed it was wet in the chamber,I poured water into the inlet tube blocked the outlet with my finger and blew into the inlet,low and behold water was seeping into the chamber,though you could not see the holes,this has happened twice in three years