York Gas Furnaces: Y81E/Y91E Re: Diagnostic Codes / Fault Codes These York gas furnaces have a control board inside the furnace blower compartment that will flash a diagnostic code that shows the operating status of the furnace. Diagnostic Codes: Slow Green Normal Operation -...

York Gas Furnace: Y81E/Y91E Re: Flashing Code 4 Code 4 = Main limit switch has opened its normally closed contacts. The control will operate the supply air blower and inducer while the open limit condition exists. ► If the main limit switch opens Five Times within a single call for heat, the...