This is how this Tankless on demand water heater works http://www.tankless-water-heater.com/products.html model 220. The Mechanical Pot is used to set the water temperature. The temperature is set to the person that takes the hottest shower by opening the hot water all the way with no cold water. The flow rate on a shower head is usually 2.5 gallons per minute. This temperature ends up at somewhere around 102 degrees F. The problem is when you use say the kitchen faucet that flows at 1.5 gallons per minute the water heater does not adjust for the flow rate of the water and will do one of two things; make the water scalding hot because when you add cold water the flow rate through the water heater decreases even more. The water heater also has thermal cuttoffs on each of the four heating elements and they will cut our independantly based on the temperature in the unit as it is working. Conversly if you turn on the bath tub hot water flow rate increases, flow rate 3.5 - 4 gallons per minute and the water does not get hot enough. You can adjust the Mechanical Pot before turning on a higher or lower flow rate faucet and solve the problem. The next issue is that the incoming water temperature changes from summer to winter and this issue is repeated. I believe that this will help also if two faucets would be used at the same time which will also change the flow rate.

So my proposed solution is to take a temperature sensor in this case I was going to try and use a onewire DS18B20 and a Digital Pot with an 8052 to maintain a preset temperature of 102 degrees F at first as a fixed value and then later to incorporate a Display of some kind with adjustment push buttons to be able to change the reference temperature.

Does that explain it well enough?

What are your thoughts?

I have a BSEET but have not practiced my trade in 20 years so I am a litte out of the loop but am very excited to try and make this work.

Mike Ruoppoli