If the faucet isn‘t fixed in place, how much will it rise when the pipe is heated from 20.0°C to 88.8°C. The coefficient of linear expansion for copper is 16 10-6 K-1. Ignore any increase in the size of the faucet itself or of the water heater.
The advice of William B above is good. You usually should have a professional help with plumbing problems. The copper pipes may have a union, If so it becomes much easier to fix. A union looks like one big nut (2 or so)with two smaller nuts on either side (1 or so) If not it will take a torch, solder and some new fittings. If you decide to fix it yourself,turn off the water at the valves above the water heater. If their is a union, use two wrenches to loosen the nuts. Once undone, you should be able to undo the pipe going into the water heater. check it for any problems, rust corrosion, etc. If it is just loose, get some teflon tape and wrap it on the treads and retighten the pipe. Then connect the union back up. Make sure you use two wrenches and tighten pretty well. It is best to have help of someone who has installed a water heater or done plumbing work to help.
The change in length due to thermal expansion is alpha*L0*deltaT 16x10^-6*2.8m*68.8 0.00308m 3.08mm
