If you have tub water-divertor or the head is clogged. Most likely former.
yes but it will sound crapy, it wont have as much horse power, so it wont run at 100% ut it can run on 3 cylinders.
the outlet pipe at the base of the shower has not got enough angel for the water to run free
Yes, have you ever run out of hot water during a shower?
Defective divertor
It would have to be the controls or the shower head. Distance from the heater or size of supply lines shouldn't have much affect. The only variable would be the control or shower head and either one could have a flow restrictor in it or both.
Cold air holds less moisture than warm air. When you run the shower with hot water, the moisture condenses on the cold mirror surface causing it to fog up. If you run the shower cold, the mirror will not fog up.
the confederacy
install flashplayer.
If you wish to control the second head from the original shower control, then come off the head. That way both shower heads can be controlled from one location. Realize that the water pressure will decrease as they have a common source, which is normally a 1/2 inch line.
You can run an engine in/out of a car without a transmission. Car wont move and engine wont be mounted properly. So i suggest not to run an engine without a transmission unless you know what you are doing.
The sump should work as long as you have a strainer in the shower
Run a new cold supply line from the source. This will drain less pressure from the the cold shower line.