help with wasps

emr_2

a few weeks ago we had a wasps' nest treated by the environmental health folk. (we had found dead wasps in the spare room one morning - lots of them - and looking out the window then saw them all streaming into wasp central). two or three wasps were found in the room for a few days after that. by the way, the window was closed but as it is an old house with the original windows, they are not a great fit. anyway, we have just come back from holiday and found many dead wasps in other rooms of the house this time. we don't know where they are nesting now. they are turning up in most rooms in the house, a few each day. the guy sent by EH is not interested in our wasps indoors. just "point and shoot" his death powder at wasps' front door. anyone have any ideas how we can stop the wasps coming in and find out where their new nest is? or any other advice?? please???