1)If I live in an apartment complex, and I hold cold showers are okay on shabbos. Can I slightly open the hot water faucet in order to remove the chill of the cold water?
2)Since the apartment buildings hot water tank is so large, wouldn't it be a safek if I would be the one to cause the water to reboil?
3) and even if I do cause it to reboil, wouldn't it just be gramma? Do sefardi poskim permit this?