I have a 3DHB12N07501D York gas furnace and it is combined with a heat pump. I noticed the Gas furnace was not kicking in. So after poking around I found the light on the board was blinking 4 times. The panel says it's the high Aux or Spill limit is open. First off I do not know what High Aux would mean. I checked the switch. I am not an electrician but I learned you can use an ohm meter to check. So I tested a normal wall switch in the open and closed position and It seems the Furnace switch appears to be closed. I did buy a switch and I guess it will be a spare if this does not fix it. No sure what else to look at. Can anyone help. Thanks