Hi,

I have a Carrier furnace 48GS-036090311TP with a Honeywell T8401C thermostat. I can run the fan on continuously but when I put the Heat to ON on the T-stat, the 5 Amp fuse on the control board (LH33WP003A) in the furnace blows. The sequence is like this:

1. Fan only operation is running fine
2. Move the T-stat to "Heat"
3. The induced fan motor starts to run (for about 3 seconds)
4. The 5 A fuse blows at just about the time that the ignitor needs to turn on (combustion relay)

I checked all the wiring connections and they look fine. The lines from the T-stat to the board also appear to be OK.

The combustion relay resides on the board.

Could this be a board problem? Or is there a problem with the AC contactor? Or the 24V transformer? I would appreciate it if someone can help me isolate the problem before I spend a few hundred dollars calling the electrician or replacing the board even.

Thanks,

:confused:

The low voltage wiring might have a short in it.