One of the most frequent questions raised on the Bounder Yahoo group (Bounders@yahoogroup.com) and one I am regularly asked is "My water heater does not start, what do you think I should check?" The answer usually is "the electrical connections". I assume the propane gas valve and propane detector are on and that when the water heater switch is turned on the water heater tries to light and when it does not, leaving the warning light beside (or in) the switch on. This tells us that there is power to the system. While observing the spark lighter have an assistant cycle the switch and note if there is any sparking sound or visible spark. If not the first thing to check is determine that there is 12 Volts on the red lead connected to the white 4 prong connector at the circuit board.(see photo)
Carefully remove the white plug from the board and check to see that all connectors are clean and not dislocated from the plug. If there is power, then you have determined that power is flowing to the heater through the thermal protector, thermostat and ECO High temperature cutoff to the circuit board. The circuit board connections should be carefully cleaned with a ink eraser after removing the board from the heater. Also clean the ground connection, which is placed under the top screw attaching the board to the heater. I recommend scraping the paint in the area of the screw hole and cleaning the connector, then applying di-electric grease on the connectors to reduce the possibility of corrosion. Re-install the connector and check for heater lighting.
If there is no power to the red wire, check for power through each of the components. With the power turned off, use an ohmmeter to measure resistance to confirm that the components are providing continuity. Most of the problems with these components are with the connectors to them. Careful cleaning and applying a coating of di-electric grease will reduce the recurrence of corrosion. The last area to confirm the existence of corrosion is the connection between the Spark lighter mounting band and the aluminum heat tube near the burner. If corrosion occurs in this area then the sparker may not operate consistently, becoming erratic in cool damp conditions or overnight. Hopefully these hints will prevent a cold shower first thing in the morning.