Aqua Hot Problems

I have run into a similar situation on two separate occasions. The first time was in our first coach (2005 Fleetwood Providence)that only had a 12 gallon water heater. Water temps were never more than luke warm. Found the shower valves in the plumbing bay were turned on even though the shower head valve was shut off. This, I was told, activates the mixing valve thus making the water warm only. The second time with our current coach with Aqua Hot I found that the water valves in the rear shower were left on and the shower head shut off was activated. Released the shut off valve and turned off the water and voila.....hot water again.