I once paid $238 for a new control board in Whitehorse, YT, only to find 200 miles down the road that it didn't need one. What it turned out to be was a high resistance on the terminals coming from the thermocouple. This device is very low ohms when under normal circumstances, when it's heated, the resistance falls even more. This is what the control circuit is looking for, a lower than average resistance in the presence of flame.
So before you replace the thermocouple, chase out the wires to the control board and verify they are OK, and then clean the terminals so they make better contact. I squeezed mine so they were tighter too and that fixed the problem.
