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F3 code indicates a gas valve on without a call for heat.
Test your relay for an open circuit
I think you have wiring issues. That's what the troubleshooting flow chart is saying. Do you have a multi-meter?
I can not find a wiring diagram and I need to leave, but I'd check for loose connections and an open circuit at the relay. Especially anything plugging into the circuit board you replaced. Sorry I can't help you further, but I'd still appreciate a positive rating for what I was able to do.