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Can you give me the complete model number on the furnace? It will be on a label on inside furnace panel just above burners.Remove panel to burner compartment and look inside. The model number will help me give accurate assistance for your specific unit.
Below is a link showing where to find label with model number:
OK turn power off to furnace and back on to reset board. See if furnace tries to work or we get same code.Also let me know if you have a volt meter for troubleshooting.
OK the 4 blinks indicates that we have an open limit switch,you may have several. Lets start with the ones that are resettable. Button in center will push in and click to reset.
OK our next step is to trace the limit circuit.First unplug the plastic 12 pin connector on board and make sure all wires are seated in plug so they make contact when plugged onto board.If all are good, follow the limit circuit and check each limit in the circuit for continuity.or by bypassing each one, one at a time.
I have highlighted the circuit for you in diagram below to make it easy to find the limits.