Franke Little butler Insta hot parts?

Not familiar with that particular model, but in the instant hot water units I've seen, if a plastic fitting that is part of the plastic tank broke, it's time for a new one because it;s not worth it to replace the tank. The ones I've had generally only last 5-7 years.

When the last one died, I got fed up and didn't replace it at all. They are a nice convenience feature, but I didn't use it enough to make it worthwhile. Also, like any tank water heater, after a couple years, enough mineral crap builds up inside so the water tastes like crap. I use an electric kettle instead now.