Default [Q] Wifi problem at home

Hello,

I've recently bought a new xperia arc. I've rooted it and after that i installed several roms (4.4.2 - 4.4.3). These roms had different kernels. On all roms wifi supposed to be working, but after a few minutes it doesn't work anymore. I have to restart wifi and after that it works for around 5 minutes. (5 minutes with screen on) Now I was heading to another home and over there, the wifi worked perfectly. So I suppose the problem is caused by our router (thompson TG789vn). The stock wifi from my phone worked perfectly.

This problem was on my xperia X8 too (rooted and android 4.2), but did'nt exist on my xperia J (stock kernel/rom). A friend of mine has the same problem at our home too with a Xperia Neo (stock kernel/rom). Soo it looks like a strange problem. Can someone help me? I tried everything (statici p, google search, other kernel etc.)

Sorry for bad english