Greyed Out Wifi, Use and Care

I'm going to pick up my 2nd replacement phone this Friday. I've owned 2 iPhones over the past 18 months but unfortuntely both have needed replacing after the Wifi chip failed. Is there any speacial care I need to take with an iPhone to avoid a 3rd phone failing and needing repalcement? Are iPhones sensitive to heavy use over a Wifi network? Should I switch the Wifi off when I'm not using it to safeguard against the chip failing? I hope to use the new repalcement a little longer than the 3 months use I got out of the last replacement.

Any tips, most appreciated.