I have a problem similar to mednomann https://www.askmehelpdesk.com/heatin...re-144953.html.

I have a York furnace that was giving me a limit switch open fault, but the limit switch was closed. I have installed a replacement control board, but I am getting that rapid red flash that suggests a twinning error. This only occurs when there is a call for heat, whether that be via the thermostat or by shorting out the R and W terminals on the control board.

The furnace is on its own circuit, and the polarity of the circuit is correct.

The model number is FG8C10016MU11A
The serial number is WKLM005688

Any suggestions would be greatly appreciated.