Yes, i dont know where this plastic is involved.
About PES Google says something like that :
"Polyethersulfone (PES) is a polymer of exceptional durability, known to be less porous and less reactive than other similar compounds. It is a BPA-free plastic that is dimensionally stable over a wide range of temperatures, resistant to most chemicals, and possesses self-extinguishing properties. It can withstand repeated sterilization and is FDA approved to be safely used as an article intended for repeated use in contact with food. PES has many applications, including: Medical / Food / Bottles......"
So it seems safe.
And if it's the Mouthpiece that is in 'PES' i imagine it's really safe because it's far from the 'heat exchanger' ?
But where teflon is involved, in the heat exchanger ? Strange, in the Herbalaire it's more about 'external' parts. I'am not a big fan of teflon , but it's ok (safe & taste).
Also Sticks about your post with this avb :
It was on which setting ?