Yes, normally H signifies hot water, and C signifies cold water.
Turn the water off to the faucet. Remove the handle. The top of the faucet should unscrew to get to the ball valve. Replace the valve and gaskets then reassemble the faucet.
Your hot water line needs more insulation probably. It sounds like your hot water is cooling before reaching that faucet. It may be that the one faucet is not able to turn all the way to hot until you adjust the faucet (usually in the handle) of a 10 year old or newer faucet.
I have this problem with my shower head, what I do to fix it is turn on the sink in my bathroom to hot, this usually shuts it up
There is usually a flow restrictor in the faucet that can be removed. It should be in the center of the faucet where the hot and cold mix. As far as I know the government made it mandatory for manufacturer's to only produce low flow faucet's . Manufacture only, consumers can do what they want with them.
Do you have hot water at other fixtures in the house? If not you have a water heater problem. If yes the Shower valve needs to be rebuilt if it is a bressure balanced faucet the concentration should be on the pressure balancing spool area of the faucet.
Yes, it can also cross through a two handled faucet. Both the hot and cold sides of the faucet must be on and the flow of water must be stopped or greatly reduced on the outlet side of the faucet. This can occur when a hose with a spray nozzle is attached to a laundry tub faucet with the faucet on and the spray nozzle off, or when a shower faucet is on but the shower spray head is off. When another cold water outlet in the system is turned on then the pressure on the cold side of the laundry tub or shower faucet in question could be lowered below the pressure on the hot side and hot water can flow into the cold water side. There are faucets which have integral check valves which prevent this from occurring. WWW.WOODBRIDGEPLUMBING.COM
First make sure that the hot and cold supply lines (the plumbing) aren't backwards (hot should be on the left as you are facing the faucet) or that someone accidentally ran two hot lines. For the problem to be in the faucet itself you would have to have a single handle faucet. If this is the case the control valve is broken and should be replaced. Three handle Left= Hot Water Flow. Right= Cold Water Flow Center= Controls whether the water comes out the shower head or tub faucet. Two handle Left= Hot Water Flow Right= Cold Water Flow (Diverter Valve is elsewhere if it's a tub/shower) Single handle One handle controls both water pressure and temperature
I think to answer that, I would have to look at your bathtub faucet. Sorry.
Employ a plumber.
If you have an instantaneous hot water heater, and your faucet doesn't flow enough water it won't turn on the water heater. Thus requiring another faucet to be turned on.
The piping has to be the exact same length for each shower head from the tee where the cold and hot water feeds from the top of the diverter faucet.
You have a cross connection on a faucet somewhere in the house. That means the hot is overriding the cold because of a malfunctioning faucet. Usually happens at the tub/shower diverter if it is a single handle.