My concord cg 90 ca furnace will not stay lit after calling for heat.th inducer motor turns on,the ignitor lights ang the gas flows,but after lighting the ignitor turns off and the burner shuts down.The green troubleshooting code flashes 6 times. No luck with cleaning the flame sensor either. Is the ignitor supposed to stay lit the entire time that the burner is on?

No. The ignitor is not supposed to stay on. Where is your fresh air inlet piped to? If it is not piped to an outside "fresh" air supply the furnace "sniffer" triggers and shuts the gas valve back off. If the fresh air inlet is piped to an outside source then the "sniffer" (sensor that the little tubes run to) may be bad. I have the same furnace and ran into the same problem, but at the time my fresh air inlet was not piped outside. Once I piped in fresh air it has worked since then.