One of the things that I like about these machines is that they are fairly accurate and brew good consistent repeatable beer, as long as your recipe is sound… and sure while their later models are better like the Z1, these are still sound machines and worth keeping and brewing.
One of the most common type of error that you will get with these machines is a HEX error, where basically there is air trapped in the heat-exchanger, and the temperature sensor will detect a big temperature differential and the machine will start to make noise and the program will end, this will happen fairly fast once you start a Brew program.
I was told that in the beginning the company just put water into these units, but the machines would freeze in colder climates, so later they changed to using glycol. I just used water, but some people prefer glycol. Botton line is, if water/gycol ever leaks out and air gets introduced into the HEX, the error will come back. The Z1 machines have the pumps and all at the top of the machine, so it is much easier to get to it, you just remove the top and you have much quicker and easier access to it, but with these original machines, the pumps, boiler and heat-exchanger are actually at the bottom of the machines.
I am attaching a doc that was shared with me from the FB Group:
https://kodiakbrewing.com/wp-content/uploads/2025/09/Zymatic-Glycol-Loop.pdf
I’ve also recorded some of it when I was actually working on it and here that YouTube video:
cheers!