Most often, owners of the iPhone 4, 4s, 5, 5s, 6, 6s, 7, 7+, X are faced with the problem of non-working Wi-Fi, failure on other models Wi-Fi IC chip is much less common.
If you're facing with Wi-Fi problem, this is an occasion to think. Is this iPhone was liquid damaged? Did you dropped your iPhone? Is it refurbished or someone worked on it? On all models after the iPhone 4s, only strong impacts on the Wi-Fi chip could disable it. Problems with the Wi-Fi module can act with different ways. For example, you can't change the settings, the power button of the module turns gray and doesn't switch, Wi-Fi is caught only in the immediate vicinity of the source, or Wi-Fi speed is too slow.
NiceRepair, recommend to replace wi-fi ic chip, but unfortunately it might require 90-140$ for repairs, the results of which you will get working phone. Also, we usually provide 90 days Warranty.