I would start by performing a flow test at your shower head. Get a 5 gallon bucket and open your shower head full open and time how long it takes to fill bucket. If you fill the bucket say in 1 minute ... read more
When you see the wasps around, look at the exterior of the chimney and possibly from a ladder.
What you may see is that they are not coming down into the chimney through the top or chimney termi ... read more