IPhone 6 Wi-Fi weak?

I have an iPhone 6 and in my apartment a weak Wi-Fi reception. It already occurs when I'm only 2m away from the router and my laptop screen is between the devices. In other rooms, the signal breaks off completely. An iPhone 5 and an Android have optimal reception in the rooms. I already reset network settings, hard reset, iOS updated, DNA changed, system service disabled… Anyone left with an idea?

Same for me. In my room (1st floor) I have no Wi-Fi, not even if the door is open. It's so exciting. My mom, on the other hand, has Wi-Fi all over the house with her Huawei, even in her room, which is just above mine…