Water Heater Flame Detector
designed by Dave Johnson - August 5, 2012
  

Solution:  A battery powered circuit would be best for his situation.  The flame detector circuit could be connected to a battery powered LED flasher circuit.  The actual LED could be mounted next to the thermostat, using the same wire pathway as the furnace thermostat wires, located nearby.  A remote flashing LED would change color from green to red, whenever the flame was on.  A red flashing indicator would alert the person that water in the heater’s tank was not up to temperature and would mean that there may not be enough water to complete a shower use.  When the LED color changed to green, the heater’s flame was off, indicating that the tank was full of hot water.

My flasher circuit is shown below.  It could be housed in a plastic box with a battery compartment.  The compartment would house two AAA cells.  Two 1.5v alkaline AAA cells would yield 3v, enough voltage to power the circuit and drive the two remote LEDs.  A three leaded, two color LED assembly would be connected to the box.  A miniature twisted shielded cable would link the box to the LED assembly.  The assembly could be some 100 feet from the box.  Another twisted pair of wires would like the box to a phototransistor, which is positioned through a hole, which can view the light from the gas flame.  The device can be 12 inches from the flame.  Be sure to use a hole which is not too close to the flame so the device will not be subjected to too much heat.  The 3v battery in the flashing circuit should be able to power the circuit for about a year.