Goodman ignition problems.

[Keith]

I have a Goodman gui075-3. The piolot does light, the flams sensor is not cracked or damaged, however the gas valve will not open. If I tap on the grey control module in the furnace, it normally will light. Sometimes it will work fine for days, other times, like tonight, I will have to go downstairs and hit it every time. Iam thingking it is a bad control module, but unsure. Any help would be greatly appreciated.