Recirculation Pump Timer

I have a tankless water heater which allows non-stop hot water to my home, and only takes up a small footprint in my garage. Sadly it can take forever to get hot water initially, and to circumvent wasted water, my home has been fitted with a recirculation pump that pumps cold water out of my hot water line and flows it back to the water heater. The way my water system works is pretty simple:

  1. Water enters the house.
  2. Water then splits into a “cold” line and through a one way valve to which is referred to as the “hot” line.
  3. This hot line is actually one large loop, containing the heating element, the faucets/etc, and the pump.
  4. The pump is triggered by two wired momentary switches and runs until a thermocouple on the return senses a temperature threshold.
  5. Water pressure is maintained by the pump being off.

The problem with the system is these buttons are limited to two and only available in the master bath and the kitchen. It would be ideal if I could trigger one of these buttons on a scheduled timer, such that there is an period of hot water in the morning available in the pipes, where it doesnt have to be managed through the button.

The parts that will be required are:

  • microcontroller (low power)
  • real time clock
  • coin battery
  • relay