do you have a multimeter * with no call for heat, measure between 'w' and 'c' as the duke said. if you do not follow, call a quallified technician. sounds like you have a safety hazard. also, we do not repair circuit boards at component level because the external safety devices and sequence of operation is programmed into the board. we replace the board. in your case, you may have wires shorted together between the thermostat and the furnace or a defective thermostat. the warning you are getting is to let you know that sequence is being compromised and there is a hazardous condition.