Some time it's the water regulator pressure valve and the pressure is high enough to trip your hot water heater valve. Might want to go outside and check how much pressure is coming out of one of your water spigots before replacing the valve on the hot water heater.
I had mine replaced last year with a 50 gal electric (including a new expansion tank) and it cost me $675.00. I used Greenlee Plumbing. They are in Braselton and not sure if they cover your area. They have a website and phone is 678-386-7513.
Wow, great opportunity for someone. I have done that job many years ago and I really enjoyed it!. (Don't have to pull the pin on when unhooking from the trailer).:)
I wonder if it is cracked and you are getting tree roots coming in and blocking it? That happened to me and I would clear it and it would be fine until the roots got back into the pipe.