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The importance of learning the laws of Shabbat
''It is impossible for a person to avoid desecrating Shabbat if they do not learn all the laws thoroughly. Unless someone has studied the laws of Shabbat two or three times, he will inevitably end up desecrating Shabbat.
"One should study the laws of Shabbat on a consistent basis, preferably with a rabbi who will clarify everything, until they know them thoroughly and with perfect recall.
"For this, one's reward is great, and the learning will protect against grave misfortune."
(Rabbi Yehonatan Eibeshitz)
Practical halachah according to Rabbi Ovadia Yosef's rulings
Is it permissible to use hot water that was heated in a boiler on Shabbat?
It is best to be stringent and not use hot water that was heated in a boiler, even if the boiler has since been switched off. (Using hot water while the boiler is switched on is forbidden.)
When does this apply? If the water is hot enough that one would instinctively take one's hand out of it, it is better not to use it. If the water is not that hot, one may use it for washing dishes or any other permitted purpose.
Is it permissible to use water that was heated by solar panels on Shabbat?
It is permissible to use water heated via solar panels on Shabbat, for washing dishes or washing one's face, hands, and feet, since the water was heated by the sun's heat, and cooking by direct sunlight is permitted.
