I would like to confirm that I understand things correctly. What I understand right now is as follows:
- Cold Water is not problematic on Shabbos or Yom Tov
- Hot Water is a problem of heating directly on both Yom Tov and Shabbos (as opposed to a water heater with a tank, where the heating is a gramah and therefore permitted on Yom Tov but prohibited on Shabbos)
So, if someone has such a water heater installed in their house, there is no problem going there, for example, and using the cold water from a faucet?
In addition, the hybrid system including both tankless and with-tank units, which could be thought of as problematic for hot water on Yom Tov, would be an issue (from the linked Star-K teshuva) only if the sensor is extremely responsive and there is no delay between turning on the faucet and pouring the cold water through the tankless component, thereby heating it without a gramah. But even in this case, turning on cold water is not going to be a problem.
Please confirm or correct this, if possible. I would appreciate any sources dealing directly with the issue, if you know where to find them. Thank you very much.