Condensate drain problem on Firebird Enviromax C26?

The drain cup leaks a white froth/foam which gathers in a pile underneath and dries to a white powder.I'm worried that this is going to prevent proper drainage. I have not been able to get a satisfactory explanation from the engineer at each annaul service.
I also have to clean the photo cell before a service is due. Any help gratefully received.
Chris