I had posted the website in the other thread and was a little disappointed that you did not try harder to follow up. For what you are trying to do, ALL information on the unit is valuable - user guide, schematics (of course) and so on. This is especially true if you want to try to reverse engineer the board toward reprogramming the PIC or otherwise get it working again or building a new board.
Look hard on the site. Write them, several times if they don't response (giving them some time). If they don't have any information, ask them who might. Wherever plumbers and pipe people congregate, make a few inquiry posts.
It's a great project, if you can pull it off. Making your own schematic could be tedious and difficult for you, but I am not suggesting that you don't do that. I am suggesting that you have not yet done all that you could before doing that, or even while doing that.
Soap Box: Not too long ago, I repaired a function generator that I had been given over 25 years ago - so long ago that I wasn't even sure who gave it to me (likely someone throwing it out). I wrote the company asking for help. I even asked if it was OK with them if I posted a schematic on a site like this one. They tried to be helpful and actually agreed (grudgingly) to let me post the schematic. Happily, I never had to as I replaced two chips and used a can of spray on all the pots and built a new power supply as an alternative to batteries. I would love to read a similar success story from you.