TM 10-7310-241-12&P 4-10.1  TROUBLESHOOTING INSTRUCTIONS FOR MODEL 471012 (Continued) 4-8.2     Change 1 Problem Probable cause   Solution Circuit board is defective.   Replace circuit board. HWR does not heat in either Voltage at HWR is low.   Start engine of vehicle.  If necessary,   setting. Green light illuminates,    check vehicle charging system.    white does not. Thermistor wire is broken. Rewire or replace thermistor Circuit board is defective. Replace circuit board. HWR does not heat in either Heating element is burned out. Replace heating element. setting. Both lights illuminate. HWR functions correctly in one setting but not in the other. Switch or switch wiring is defective. Rewire or replace switch. Circuit board is defective. Replace circuit board. HWR heats in settings I and II.    White light is burned out. Replace white indicator light. Green light illuminates; white does not. HWR heats in settings I and II Green light is burned out. Replace green indicator light. White light illuminates, green does   not. Circuit board is defective. Replace circuit board. HWR only heats water lukewarm. Thermistor wire is broken. Rewire or replace thermistor. White light does not cycle on Thermistor not firmly secured to    Re-mount thermistor firmly to wall. and off when desired temperature is reached; water temperature is excessive in wall of container. setting I or Setting II. Circuit board is defective. Replace circuit board. HWR takes excessive time to Heating element defective. Replace heating element. heat in settings I and II. Both lights illuminate. Thermistor wire broken. Rewire or replace thermistor. Circuit board is defective. Replace circuit board.