Water – What could be causing low hot water pressure to a sink

I would first flush each feed line by detaching them from the faucet and opening them to flow into a bucket until the water moves freely.

Then if you have any compressed air, you might be able to blow out the faucet backward (blow into the faucet outlet/aerator end). This should blow any calcium debris out the rear of the faucet. Of course you must open the faucet valve so the air can pass through it. With luck, that will clear the faucet valve.

Then re-attach the feed lines and confirm that water flow has been restored through the faucet. Of course if calcium continues to dislodge in the water line, the blockages may recur.

Some toilet valves can be taken apart to flush the sediment out. Turn off the valve that supplies the toilet and flush it. This will allow the fill valve to depressurize. I have been able to clean two types. Both had some arrows / instructions, one you pushed down and rotated the top of the fill valve and it pulled straight up then slight turn the water on--this clears the stuff in the line (I found putting a glass on top allowed me to turn the water up and really clear the line).

The second type I have only had ~75% luck with they have 2 plastic clips that you slip a small screwdriver under and lift the cap same as above for flushing, but use caution the plastic breaks very easily and a valve replacement is needed. As for the other valve / tub, if it has a shower head or arrestor they need to be cleaned also. If it has washerless valves you may need to disassemble the valve flush and reassemble.