Originally Posted by Scheinin
I am not sure what you mean by "cartridge" I traced the hot water line, as best I can, from intake to spicket with no hinderance. I suspect the problem is between intake and instant hot water heater.
The cartridge is the part in the faucet (inside, under the handle) that controls the water flow to the spigot when turning the handle.
Often times, debris (sediment, shavings, etc.) can lodge inside the cartridge and plug it up and water will not flow.
(or flows very slowly)
You will need to disassemble the faucet to see if that is the problem. Usually if plugged and not leaking, they can simply be cleaned, rather than replaced.