I have a Goodman Model # GSM100-4 furnace that has been a pain the tail. This week I went to start it up and I am getting a constant flash on the control board. I have an old, what I thought, was a good board that I swapped out. Still the same problem, constant flashing. I tried swapping the control transformer leads around- no luck. This unit worked fine this spring when we switched to cool.
The unit will go through it's normal start-up procedure with the blowers running, ingniter coming on, gas valve opens flame, ingniter goes off and within a few seconds the gas valve closes.
So far I replaced the flame sensor. This was before I noticed the flashing led. This was the problem on start-up last year and the reason I have another what I think is good circuit board.
All wiring appears to be good and tight, all connections sprayed down with contact cleaner.
Any help would be appreciated.
Thanks in advance,
John

In order for your flame sensor to sense a flame your gas manifold or gas valve will need to have a good and true equipment ground.

The flashing is a code telling you something, kill the power for a few minutes then back on,, count the flashes and look on inside of the cover and see what the code is,, to do this you will need to peep through the sight peep hole or hold the cover/door button in manually to see the blinking light

Thanks for the speedy help. The constant flashing code is incorrect twinning? The cure according to the door panel is to reverse the polarity, which I tried yesterday, to no avail. One thing I did forget is that I did find the ground wire going to the AC motor contacter was disconnected yesterday. I hooked that up, knowing I had found the problem! No luck.
I put the meter on it this morning and I have a real good ground on all componets going to both the netural and the ground.
I think the problem is in the flashing issue. Perhaps something to do with the ground wire coming off the AC?
Help- it is going to get cold starting tomorrow!
John

Make sure your thermostat is wired correctly to the furnace board. If it is a single furnace, there should be no wire connected to the twin terminal on the board. Other than that it still sounds like a bad board.

The thermostat wiring has not been changed. There are no wires on the twin terminal. Is there any other thoughts on the board being bad? Every thing appears to be OK- grounds- A-OK.
Thanks,
John

Thanks for the help folks. Turned out the board was bad. Got lucky in that I replaced the board a year ago, and Johnstones gave me a warranty on it. Had one week left until it was outa warranty!