This is an old thread but it helped me. We had a leak under the kitchen sink, somewhere. There's a leak it turns out on the hose for the sprayer. 'kind of where it forms a 'U' near the weight. We have a Kohler K560 CP. (one handle for hot and cold) For some stupid reason I shut off the hot and cold valves under the sink. But it was nice that after 3 years they were not frozen at all. So im using a bucket under the leaky line until I get the replacement hose. ANYWAY, when I turned on the valves and the faucet, hot did not work at all, and cold worked normal. And then I lost some pressure on the cold. So I eventually tried what was recommended in this thread. I shut off the hot valve under the sink and I detached the hot line at the valve point and put it in a bucket. The cold valve was open, and I opened the cold full blast at the sink and held my hand tight over the faucet tip. I did that a few seconds. I was glad to see water and sediment had shot out of the hot line into the bucket. I reattached the hot to the valve and opened the valve. Both hot and cold water flow were restored. So I haven't flushed out the cold line because I dont want to break what isnt broken. :)

Electrical will not effect water pressure (unless there's a pump involved). Here's some possabilities. Trash might of been stired up and plugged all 3 facuet airators remove one or more to see if pressure returns. IF there's a backflow valve or pressure regulation valve in the hot water pipe,that could be stuck. IF you turned water supply to heater off at a valve that controls hot but not cold water,the was,her inside may have cracked or come loose or "gate"might have dropped(come loose)on gate valve. See if valve still turn's hot water completely off and on. If it doesn't,turn off water at main or meter then dis-assemble valve for inspection. If you only turned water off at main or meter,disregard above. Let us know what you find.

Your builder is handing you a lot of BS there. These units are never considered a “necessary” luxury. Do you have the Sub Zero refrigerator? Pro style range? In some locations, those would be considered necessary at a certain level of build. A hot water dispenser? Ah, nope. Having had had one prior, it didn’t make it to the next kitchen. When you find yourself making excuses to use it, and those excuses are few and far between? Plus, to make tea, you want fresh oxygenated water heated to just shy of the boiling point for the best flavor. A freshly filled electric kettle is as rapid as happens for a pot of tea. For a cup, the microwave is the quick solution. Now, I collect tea pots, and have a whole cupboard of different teas, so someone who isn’t as fussy about it could be perfectly fine with an instant hot. I put that instant hot money into a whole house tankless water heater.

When you said you took "the faucet completely apart," does that also mean that you pulled and inspected the cartridge. I had exactly the same problem once and finally found that the problem was a chunk of grit that was pretty much blocking the hot water port: it was trapped in place by the faucet mechanism, but came out easily once the cartridge wasn't blocking it.