[techiemike]

American Standard Freedom 90 VS furnace (city natural gas supply)
model AUY100R9V4V0
SN N411SX47G
Furnace has a problem with all burners lighting. When call for heat is presented, ECM motor blows properly, igniter turns on & glows bright orange, gas control valve opens, and flame starts at burner next to igniter. However, the flame does not always travel to burners farther down the line, so the flame sensor does it's job and shuts the gas valve off. If all burners don't light after 3 tries, the control board does it's job and shuts down the ingition process (3 blink code displayed). I have not found any blockages in burner passages. When all burners light, furnace works properly, but I have to cycle power to reset the ignition circuit at least twice a day. Flame sensor has been cleaned and appears to work properly, and both overtemp sensors are at 0 ohms (closed). No other error blink codes are displayed, so I'm assuming the 2 pressure sensors are also OK. I suspect a problem with the gas control valve. What else might cause this burner issue? Is there any way to test the gas control valve ? Can the control valve be adjusted/repaired, or must it be replaced? Any ideas greatly appreciated.

 

[techiemike]

edit to post

my bad - the furnace gives a 2 blink code, not a 3 blink code when the control board locks out the ignition circuit.

I did clean the flame sensor and all burner slits - no noticable effect - was there a problem with the gas control valves on 10 year old American Standard furnaces? I also reseated all the connectors on the headers of the control board, but did not clean the connections - could this issue I'm having be caused by a poor electrical connection ?

 

[kenmac]

can you hear gas comming out of the burners that aren't lighting. Try a long match stick it next to the burner that isn't lighting. If it or they light . You have blockage in the burner cross overs somewhere keeping the flames from jumping over to the next burners