I have a trane xe80. Approximately 13 years old. Heater will come on but occasionally the blower will not turn off after the heat turns off. The light flashes five times. Code indicates flame sensed after gas valve shut off. Could this be caused by inadequate air flow? I have a merv 11 filter at air inlet. Furnace has electronic air filter that was dirty but has now been cleaned. Furnace worked OK for several days after cleaning electronic air filter but malfunctioned again yesterday. I removed merv 11 filter and put in merv 8 but have not tested yet. Thanks for any help.

This condition is pretty rare. Either the gas control is sticking open or the gas valve relay on the circuit board is sticking closed. You will need a voltmeter to rule out the board... got one?

Thanks for your response. I assume the board will need to be replaced if the problem is the gas valve relay? Sounds expensive.

I assume the board will need to be replaced if the problem is the gas valve relay? Sounds expensive.

You are correct on both counts - IF the problem is the GVR. That's where effective troubleshooting comes in...