Its a bit old, hope it still helps.

My experience after using having it for 25 years on multiple properties is not worth to fix and even recommend to remove it.

My reason being these tech are just outdate and typically cheaply designed by OEM.

Instead of instant heater, I strongly recommend tank heater if you have the budget. You get to enjoy the hotel style shower everyday.

no other way than buried in the hot water line if you do not already have. I do not recommend exposing hot water pipe. 5 years ago I did mine 2.5k each bathroom, including tiles, copper pipe, mixer tap, hacking and recover and tank installation.

If you are moving in a new place, then its a good opportunity.