P a g e
10
CIRCUIT BOARD OPERATION
When the user opens a Hot Water faucet, water starts flowing through the unit and activates the
Flow Switch which in turn activates the Relay; this applies 12VDC power to the ECO (Emergency
Cut-Off Thermostat) and to the
“Heat Demand” Connection (5) of the Circuit Board (see below).
Change to: ….ECO (Emergency Cut-Off Thermostat) and to the ‘TH’ Connection (2) of the Circuit
Board.
Power is then applied to the Sail Switch that is open when there is no air flow from the blower.
The ECO is normally closed. The Circuit Board starts the blower and verifies that the Sail Switch
closes: when this occurs the Circuit Board will sense the 12VDC at the Circuit Board indicating
that there is sufficient air flow for combustion. The circuit is now complete.
Try For Ignition (TFI)
The Circuit Board is now ready to try for ignition and applies power to the gas valve through
connection (4) and without delay generates a spark of five (5) seconds duration at the igniter. If
the Circuit Board does not sense flame at the spark igniter, the gas valve is de-energized and
an internal post purge of 15 seconds will occur before a second try is attempted. Two additional
tries will be attempted and if no flame is detected in the process the Circuit Board goes into
LOCKOUT mode and will make no further attempt to light. Once the system has entered lockout
mode, it must be reset. To reset the water heater, turn OFF power to the water heater OR close
the faucet (removing the demand for hot water for a period of five (5) seconds.
Figure 6