Dear Brigita, I guess that  ...

Dear Brigita, I guess that  the pseudomonas is within the biofilm?

I looked up some advise from the Environment agency in Germany. Thermal and /or chemical disinfection is suggested. Often a thermal disinfection is not suitable. If the chemical treatment over 4 weeks is not sufficient and regrowth appears (what happens in your case). The last line of defense is the change of the contaminated parts.

Any idea of the source? If chnging the parts you could install at the POU Filter plus UV to ensure safe water for the customers/users.

My 2 ct's. Wish you a lot of success.