Pilot won't light M1GB 056A BW

[Mandy]

This furnace ran perfectly the past two winters, and the pilot flame was always quite large and very blue, no other color.
Today is the first time I have tried to run the furnace since last spring. I didn't bother shutting the pilot off during the summer. I checked the pilot before turning on the thermostat and found it was out, which I thought was a little odd seeing as the only time it has ever gone out in 2 years was when I shut off the gas, and I hadn't done that since I last ran the furnace.
Anyhow, I lit the pilot, and while I was holding the control in the "SET" position the flame would burn, with the same large, blue flame. But, as soon as I released the control back to "PILOT" the flame would go out. I tried holding the control in the "SET" position for longer periods of time up to a couple of minutes, and the pilot goes out as soon as I release the control.
What do you think might be the problem?
Thanks in advance for your help.

[Robert]

Most likely a bad thermocouple.


Thanks,
Robert