In my 3 story TH, I have washer/dryer with water heater on 3rd floor. Hot water will flow into the washing machine, but I am not getting the hot water anywhere in the rest of the house. I would think the water heater wasn't getting cold water inflow if it wasn't for the fact that the hot water comes out in the washer, albeit slower than usual. Turning on the hot water tap only in the downstairs faucets, results in a tepid, not cold, slow flow of water, which keeps you from freezing your butt off when taking a shower, but is hardly enjoyable. What is going on here?

Remove one shower head and run water through shower arm. See how much water flow you get.