The pressure of the hot water coming out of all of the faucets in my house is very low. Including the dishwasher, washing machines and shower heads.

What could cause this problem?

Could be sediment from your heater getting caight in the heat nipples of the heater. Do you flush your heater periodically? Open the drain spigot to see if you get a real good flow down there, if you do then we are going after the nipples. Check all arerators and the screens in the washing nachine supply hoses. If sediment is caught in the nipples there will be some in all areators and screens too. Back to you

I agree with Ball. Most likely the nipples on top of your water heater are clogged. I would suggest replacing them. You could clean them, but they are cheap and once you have the old ones out, its just as easy to install new ones. If you would like further info as how to clean or replace nipples, just let us know.