I believe you've got something clogging it up somewhere. When you have all faucets shut off, pressure will come up to full pressure everywhere in the system (let's say 45 psig) because the water will trickle through the clog until it pressurizes the downstream side of the clog to 45 psig, then flow will stop. When you open the hot water faucet, you get hot water at 45 psig, but that pressure quickly drops because the clog is causing a pressure drop at the clog, and then you just get whatever flow the clog will allow.
If all of your hot water faucets are doing the same thing, I'd say you have something clogging your HWH hot water outlet valve, since it's common to all the faucets. If only one hot water faucet is doing it, then that faucet has something in it.
1988 Coleman Sequoia - popup (1987-2009) - outlasted 3 Dodge Grand Caravans!
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