Here it says that that Achazyahu fled via Beis ha'Gan. In Divrei ha'Yamim II, 22:9 it says that he hid in Shomron, and they brought him to Yehu, and killed him there!
Rashi: He fled via Beis ha'Gan from Yizre'el to Shomron, and Yehu chased him 1 .
Rashi citing Sanhedrin 102b: [Divrei ha'Yamim hints to his evil. He used to hide in Shomron from Sarei Yehudah, because] he would erase Hashem's name from Sifrei Torah, and write the name of idolatry in its place.
Radak: They struck him on the way, like he said "Hakuhu El ha'Merkavah." He fled, stricken, to Megido. He did not truly die; rather, he could not speak due to the blows. Also "va'Yames Libo b'Kirbo" (Shmuel I, 25:37) does not mean that Naval died. He died only 10 days later! After, Achazyahu's servants carried him to hide from Yehu in Shomron. Yehu's servants chased him, found him hiding in Shomron and brought him to Yehu in Yizre'el, and killed him there.
Malbim: He was hiding in Shomron, and after Yehu came to Shomron, Yehoram went to flee to Megido. They caught him in Megido and brought him to Yehu, and he killed him there! In Divrei ha'Yamim, Ezra filled in matters omitted here.
Rashi: This is difficult. Yehu did not rule in Shomron until the next day (10:1)!
Why does it say "b'Ma'ale Gur"?
Rashi: There they brought him to Yehu.
Radak: That is where they struck him while he was fleeing. "Va'Yakuhu" is omitted from the verse. Since the verse said that he commanded them to strike him, it is understood. Many verses are like this.
