What could cause loss of hot water pressure throughout the house all of a sudden and how do you repair it?

If you have alot of fine sand in your water as we do, it could be that as the water heats it cooks the sand onto the heating coil and therefore narrows the space the hot water travels through. It does not affect the cold at all only the hot. If this is the case you need a new heating coil for your furnace. The only thing we've been told helps slow this down is to install a filter for your water as it enters the house. We have done this and it does remove alot of the sand but evidently not all! Good Luck!

***This just recently happened to my hot water but it started in tub one day and then the next day was sinks and it turns out that it was from the pipes we had. He had galvanized (not sure on spelling) and they tend to rust a lot and narrow the opening of pipes and then chunks of the rust come loose and block the already very narrow pipes. Then you have no water pressure because it cant get through... you can sometimes see if this is the problem by taking a hammer and tapping on the hot water pipes all the way from the hot water tank to the faucets while the hot water is running. If you get brown water or the pressure gets better or worse than that's most likely the problem.