Does one have to respect his grandfather? [duplicate]

Question

Does one have to respect his grandfather as an extension of kivud av va'em or for any other reason?

Answer 1

Kitzur Shulchan Aruch 143.20 says "You must honor your older brother, regardless if he is a brother from your paternal or maternal parent. You must honor your father-in-law and your mother-in-law (as we find that King David, peace be upon him, honored King Saul, who was his father-in-law and called him, "My father," as he said to him, "My father, see and observe"). You must honor your father's father but honor due your father exceeds that of your grandfather."

This is based upon the Rema "And some say that a person is not obligated to honor his grandfather, but this does not appear correct to me. Rather he is obligated in the honor of his father more than that of his grandfather (Maharik, Root 44). (And the proof is from the midrash regarding [Gen 46:1], "and he offered sacrifices [to the God of his father, Yitzchak]")." (HaMapah on Shulchan Arukh, Yoreh De'ah 240.24)

the Gra says "it appears that the mother's father is not included." Bei'ur HaGr"a YD 240:34 (thank you for the source Fred!) The Gra cites this story (Sotah 49a.11) as a proof for this concept.

These treatises (given by Fred in the comments) address the question very well, they give a much more encapsulating review of the available sources:

Honoring Grandparents - Dinonline, Harav Yehoshua Pfeffer ;

Honoring Grandparents - Rabbi Aryeh Lebowitz