Bryant - sporadic lockout
I am looking for help with a 7 yr old Bryant furnace, Mdl 310AAV066135. About 2 wks ago during a sub-zero cold snap, I found our furnace in a complete lockout flashing error code 21 - Gas Heating Lockout. After re-setting the power to the furnace, it fired right up and didn't have any issues until last night. Last night, I caught the furnace in a temporary lockout flashing error code 34 - Ignition Proving Failure.
After re-setting the power, I watched the start-up and caught the furnace attempt to light with only the 2 burner tubes around the igniter lighting. There are 6 burner tubes total. The furnace did this 3 times and on the 4th attempt, the furnace lit and has run without incident overnight.
I have cleaned the flame sensor with steel wool, the filter is changed regularly (current filter has been in 3 weeks) and I changed out the igniter 1 yr ago.
I get the feeling the gas control valve is going bad, but am unsure. Any ideas or do I need to get a repairman out to look at it. I'm a firefighter and am gone on 24-hr shifts. I don't trust the furnace anymore and am afraid it is going to lockout one of these days when I'm not home! Thanks for your help.