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furnace wont stay lit

1400 Views 4 Replies 4 Participants Last post by  oncall
it started out as it would have a hard time lighting it would take 3 or 4 cycles then it went to lighting for a few seconds then turning off the burners and go into watchguard mode. so i cleaned the flame sensor this seemed to fix it for a few heating cycles. i then replaced the flame sensor, now i get nothing not even opening the gas valve. so i switched back to the old sensor and it tries to light but wont stay lit. so i checked the pressure switch it is working i cleaned the hose and the condensation tube. now here is where i get confused, with the old flame sensor in i can jump the gas valve manually when the ignitor is at full temp and get it to light and stay lit with the jump, if i leave the jump on for 3 or 4 min. then remove it the furnace will stay lit in normal operation. if i shut it down and re start a few min later it will run normal operation, but if i leave it for 20 min. i will revert back to the symtoms above. with the new sensor in i cannot jump the gas valve and keep the fans on they shut off and the leds tell me the board is wired wrong. help please.
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Furnace won't stay lit

Sounds to me as if it might be the gas valve. What is the model and serial number and make of the unit?
lennox g50uh

i will be cleaning the burners shortly and i checked and cleaned all the grounds
Hello new here but I like to help

Check the gas valve connections are making good contact.
Make sure you have voltage at the gas valve and it is constant not intermittent when you are calling for heat.
If the voltage is constant and the burners do not stay lit it sounds like the coil in the gas valve is weak and the valve will need replaced.

If you have anymore information it could help out.

Hope I was able to help you.
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