Don't know if the problem is solved by the time I am writing this thought.....hope so.....it is a dangerous problem and should be solved asap.
My guess is, something happened during the replacement of the the new unit.....like there must be something blocking the common vent...is there a...
I think you can use a common expansion tank (diaphragm type, rated for the application temprature) which will eliminate the problem of solution of gases in process water and further will result in a much smaller tank without the need to install the tank at a high elevation.
You will need a...
