RO/DI setups

[hillegom]

I have looked at the second link again, the one with the plumbing connections.
Seems you need to install that check valve. Make sure that its in line properly, not reversed. It needs to be able to flow towards the RO membrane.

If water is constantly flowing into your drain, even when the RO water is shut off, as at that time when the float valve shuts the ro off, Then the only shut off you have left that is supposed to be working is the electrical solenoid. This should be shutting off the incoming water.
Because you do not have a check valve installed, the system will not hold pressure and the solenoid will never think that enough ro water is made. So the solenoid will reopen and the pump will turn on trying to make more ro water. But the float valve is closed, so everything will go to the drain. The flow restrictor will allow water to flow slowly to the drain, finally releasing pressure in the system and the whole operation will repeat
Install the check valve would be what I would do