iPhone 5c searching for signal

Ok so my iphone 5c has been working fine the past 3 weeks, full signal when I should have had it. On Thursday last week I let the phone completely die, then when I turned it on it said searching in the top left. I took the sim out and it didnt make a difference, the no sim card warning did not come up. I turned phone on and off still no luck still said searching. I then decided to reset the phone. still no luck. I then decided I would completely restore the phone to factory settings. I did this then the phone got stuck and would only load 60% of the process, it would not do anything then i decided as I read about people doing it i would try using a hairdryer to warm up the back of phone near simcard slot. I held hairdryer for about 30secs this allowed me to get past the restore settings and set up the phone. Vola the phone had signal again. However within 1min the signal was back to searching... I then tried again heating up back of phone with hairdryer and again the signal came back to full bars.. But again within 1-3 mins the signal reverted back to searching. The only way to keep signal on phone is by constantly keeping it warm. Can someone tell me what is causing the fault? baseband chip? Is there a permanent solution?

Thanks