Rav Sternbuch (4:209): In Kiddushin (31b) it mentions that R’ Yaakov’s father and mother both poured him a drink. The gemora concludes that he should take the drink from his mother but not from his father since his father is a talmid chachom he will be insulted if his son accepts the drink from him. In other words, since his father is a talmid chachom who wants to serve his son and the son agrees to accept his service – it will make his father feel insulted. These words are astounding! We have a case where the father wants to do something for his son so why would he be insulted if his son accepted his offer? Was his father just trying to test his son to see whether he would accept? Consequently this halachic conclusion must only be in the case where the mother is there and wants to help and but the son would rather accept it from his father. In such a case it would appear that since his father is a talmid chachom it would be degrading for him because the father is being treated as equivalent to his mother. That is why he should take the drink from his father but rather he should take it from his mother. It would follow from this analysis that if only the father was offering a drink then it would be permitted to take the drink. With this explanation, all the questions of the Maharsha on the gemora later regarding where the father is not concerned about his honor that it is not a concern and that the son is permitted to take it. However there is a problem with this answer since Shulchan Aruch (Y.D. 240:25) doesn’t make this distinction and simply says that if the father is a talmid chachom that it is prohibited for the son to accept the drink. That is because if he allows his father to serve him it seems that he is insulting the father’s Torah. Thus it seems according to the Shulchan Aruch that even if the father is forgiving of his honor and really wants to serve his son, even so if the son accepts the drink the father would be insulted. This is in according with the text of the gemora here. This matter in my opinion requires great study and it is an astounding innovation. (Look at the Birchei Yosef in the name of the Pri Chodosh that he should not accept even if the father is very insistent). Perhaps this is true only if this is done on a regular basis then we should be concerned that once in a while he might be insulted. It would follow that it is always prohibited to accept service from a talmid chachom because of the possibility that he would be insulted when someone accepts his offer. In other words even if the talmid chachom really wants to be of serve it would be prohibited to accept the offer just as it is here concerning a father who wants to provide service. Nevertheless the Shulchan Aruch rules that it is prohibited unless you want to conclude that it is only prohibited if it is done on a regular basis. This matter requires further thought. That is of course referring to any Torah scholar who wants to serve others but a student who wants to serve – it a is mitzva to accept as in mentioned in Chazal.