Troubleshooting Carrier Furnace on Startup

[jeffc]

My Carrier furnace starts up normally (thermostat working, blower on, ignitor glows, flame comes on), but shuts down after about five seconds. Replaced flame sensor with no effect. What other safety mechanism could be causing the gas to shut off after only a few *

[juster]

lack of proper air flow, did you check your air *

[heatseeker]

is there a good flame at the *

[Freon]

Shutting down so quickly could indicate either a flame sensing issue or a draft inducer pressure issue. If you can follow theduke03's recommendations you may have less testing to do. But since you replaced the flame sensor you could try TEMPORARILY jumping the pressure switch on the inducer blower. If that stops the problem, then check the flue for any type of blockage.

Lastly, if the inducer and flame sensor are good (new), then I would suspect the control board, especially if it's positioned close to the firebox (excessive heat kills electronics).