My Carrier 58SS gas furnace starts up and lights up the burners and operates normally for 2 minutes, then the burners shut down but the igniter and pilot light continue indicating the thermostat is requesting the furnace to heat up the house. I changed thermostats to see if that was the problem and it isn't. When I shut off the furnace and retry it the same thing happens in the same amount of time every time. For some reason the gas is being shut down to the burners after 2 minutes. I replaced the air filter and checked the reset button used for a blocked air intake. Why is the gas shutting down to the furnace burners after 2 minutes? Thanks.

The WB

Your limit switch may be malfunctioning. Do you have a pilot light or an electronic ignition? I don't think that you can have both.

labman

Does the blower come on? Gas furnaces have a start up sequence with sensors checking each step. If something doesn't work, it starts over again a few times before giving up. Some furnaces use an electric ignitor to light a pilot, and then open the gas valve once the pilot is burning. Then a sensor must detect a flame. The next step is for the blower to come on. If either it doesn't detect the flame, or the blower doesn't come on, it shuts the gas off and tries again. The problem could be either one of the switches, or on the control board. The relay for the blower on the board often fails.

Many newer furnaces have a light that flashes a trouble code. Could help yu narrow the problem down.

David Pollard

Yes the blower comes on and a check of the heat vents shows normal heat being distributed to the rooms in the house. There is a pilot light and I can hear the ignitor until the burners light off. 2 minutes later the burners shut down and the ignitor can be heard again.

labman

The circuit board is shutting down the furnace because it thinks the blower isn't running. Either the limit switch that signals the blower is running is bad, or the board is bad. The limit switch will be a thingamabob somewhere on the heat exchanger and have 2 wires running back to the board

The WB

Are your thermostats level?

Tarik

I have the exact same problem though our furnace run for more than 2 min at a time. I
Did you figure out the problem David?

BrianM

I have a very similar problem but not as severe. A tech guy came to replace the blower motor and the problem got worse. He thinks it could be the spark sensor or gas value. He also recommends replacing the whole thing. What was your solution? I see the spark sensor costs is about $25 and I may go with that. The heating season is now gone here so I could wait till fall.

hvacservicetech_07

brianM, I would suggest cleaning the flame sensor before you call somone back