have heat recovery unit on a/c the only time it supplies hot water is while the a/c is on but it does not seem to heat the water in the water heater tank, IF running hot water while the a/c is on we get alternating temp water that fluctuates ever 15 to 30 seconds from omg cold to scalding hot. it makes taking showers frustrating.. no matter how long no one uses hot water there the heat recovery unit does not seem to heat the water in the tank and while using water while the a/c is running it seems to just come off the top then pulls cold from the tank, so far i seem not to be able to explain the problem well enough that anyone investigates beyond the water heater which checks out fine as far as the heating elements are concerned(temp is set to the 125 recommended by the heat recovery unit for the a/c. the only other thought would be the tank is so full of sediment that it only holds a few gallons of water? is that even possible?(it is a 55 gal tank)