Well I woke up this morning with no running hot water and some friends told me they had the same trouble so here’s what I told them:
This only works if you still have at least 1 line (probably cold) still running, so hopefully you do. Turn on all the hot water faucets in your house (bath, sinks whatever). If nothing comes out, keep reading. Now go back and turn on every cold water faucet to a little more that a trickle. The warm air from inside the house coming in from the open faucets plus the circulating cold water SHOULD eventually thaw it out.
HOWEVER: The only problem you may run into is that when the pipe was frozen it may have burst, you wouldn’t know it yet because the ice is blocking the leak but once it thaws you could have a mess on your hands. So don’t turn on your faucets and leave, stick around for a while.
This works on cold water lines too although 9 times out of 10 the hot water line will freeze first (since hot water freezes faster because of the transfer of thermal energy, it’s true, look it up). This trick my not work for everyone but I always do it and my friends said it worked for them so it’s worth a try! Good Luck!