I need to replace the dip tube on the water heater. There is no cold water shutoff on the heater itself, does it matter where I shut off the cold?I have two copper tubes going into the top of the heater,the hot has some kind of filter or something connected to it [ brand name therm-x-trol] and it has a shutoff on that line. Also you said to turn on the hot to relieve pressure,do I leave it on while I replacing the tube? Sorry, but I'm pretty much a bone head when it comes to this stuff. Thanks for your help!

Shut off you water main and the fuel to your heater. Open a faucet somewhere to blow off pressure. I would also open and drain down the heater itself a few inches, use the drain cock near the floor. Tell us what the fittings look like on the top of yout tank, are they soldered or dielectric fittings or what?