Low hot water pressure in upstairs sink but not upstairs shower
Within the last week the hot water in our upstairs bathroom sink suddenly lost pressure. When you first turn it on after being off for a while it flows strong but as the water heats up the flow slows down singificantly however in the bathtub in the same bathroom there is no problem. Oh and the sink has separate hot and cold controls rather than a single control and the cold water works just fine. Any idea what would be causing this. I would have thought its related to a pressure problem to the hot water line that comes upstairs and feeds the sink and tub but since the hot works fine on the tubs faucet this couldn't be the case could it? Only other thing I thought was maybe its the faucet control itself but then why would there be full pressure briefly until the hot water side heats up?
You may have some floating debris (piece of interior pipe scale or part of a rubber washer or o-ring, etc.) in the hot side of the dual-handle faucet.
Turn off the water, dismantle and remove the hot side faucet body, cover it with a towel and have someone turn the water on very briefly to flush it out.
Check the washer and o-rings on the faucet body while you have it out. Replace if necessary.