First suspect: Your water heater is probably bypassed and empty The water heater in bypass (winter) mode does not mix hot and cold water, it simply routes no water thru the water heater. No water in. No water out.
Hot and cold will mix if either of the shower wands is in the "pause" position and the faucet valves are on. This is especially annoying when it's the outside wand and ya gotta go outside in the dark and rain to correct it.
If you power on an empty water heater with 120vAC the heating element vaporizes faster than you can switch it off. So even if there's water in the tank it will never heat.
Water heater has a circuit breaker on the main panes and a switch on the heater itself. Outside inside the drop down door. Should have been set Off and safety clipped in the Off position when new and I re-clip it when winterized.
And, it's a water heater not a hot water heater as there's no need to heat water that's already hot.
(Sorry, reflex reaction.)
-- Chuck