The 2a fast blow fuse blows immediately on this G20e. Can not tell from schematic what the cause might be. Anybody have this problem before. What part or parts need to be replaced? Cost of parts? (this is the fuse on the circuit board that is visible when the fron covers are off the furnace).

You have a short in the low voltage circuit. Most the times with this problem I find that something (dog or weedeater) has cut the 2 small wire coming from the inside airhandler to the outdoor conding unit or that the contactor coil is bad

Try disconnecting all the thermostat wires from the printed circuit board , these are the wires that go to the thermostat and outside unit, put a new fuse in and try it, if it does not blow the fuse then reconnect one wire at a time to determine which one causes the fuse to blow. This will point you in the direction of the problem such as a shorted wire, burnt contactor coil or relay, good luck, Mike

You have a short in the low voltage circuit. Most the times with this problem I find that something (dog or weedeater) has cut the 2 small wire coming from the inside airhandler to the outdoor conding unit or that the contactor coil is bad

ESQ1, thanks for reply. I have no outdoor unit, no central air. Furnace only.

Try disconnecting all the thermostat wires from the printed circuit board , these are the wires that go to the thermostat and outside unit, put a new fuse in and try it, if it does not blow the fuse then reconnect one wire at a time to determine which one causes the fuse to blow. This will point you in the direction of the problem such as a shorted wire, burnt contactor coil or relay, good luck, Mike

Thanks for the reply Ace. You and ESQ1 both mention contactor coil, where is this located? Also, what relay are we talking about? Is the relay on that circuit board? BTW, this unit is at my 3 season cottage 200 miles away, and I won't be getting back there for at least a week to check on your suggestions. Really appreciate the hellp/info ;))

If heating only, still is a low voltage. Check wires from the thermostat to the furnace. Make sure no wires are totching in the stat. You haven't be working inside the thermostat have you? Could be a mouse hase chewed insulation off wires

Thank you, will check on this and post back in about a week.

I used the G20 troubleshooting flowchart and identified the problem as the BCC circuit board. This is on order and will be replaced. Will update when I kow for sure if this fixed the issue.

Ok, I checked the thermostat and there is nothing wrong with it. I replaced the BCC2 circuit board with the latest level, a BCC3 card, and the furnace fired right up. If anyone has any problems with the Lennox furnace, I advise using the troubleshooting flowchart and a multimeter and the problem should be found. FYI, the BCC2 card cost about $120 plus shipping. I purchaased mine online through hvacpartsshop.com and the service was flawless.