Gas and Oil Home Heating Furnaces - furnace

I have a Goodman Furnace ( Model # GMP100-3 ) and it is being tempermental and only working intermittantly. It completely shut down in December and I had a service tech come out. He replaced the High Limit Switch and said he suspects that the Control Board may need to be replaced. Now that it is acting up again i'm curious if there could be any other causes for this problem before replacing the board. I have checked the Flame Sensor and the Ignitor both of which seem to be working normally. I took out the circuit board to check some of it's components and it seemed to test ok. All of the burners light normally but at times, once they are lit, the furnace shuts down but the blower comes on. It tries to re-start and re-light but can't. Eventually it goes into 'lock down' per the owners manual. Once the thermostat is reset, it works fine again for a few cycles, then it becomes intermittant again. I have no problem replacing the circuit board but wanted to see if there were any other possibilities that may cause this problem before doing so.
Thanks in advance for your time!

Does it have a red light that on the control board that you can see when the cover is on thru a port in the cover. If so, is it flashing when it does this?

Yes I have checked that as well and it does not blink at all. It is steady the entire time.

Just for grins and giggles try this. On my furnance in the upper area above the control panel, there is a tube leading from the blower housing that vents the combustion product that goes up to a small round switch on the left had side of the furnace enclosure. If so, disconnect the tube from the blower and try sucking on the end of the tube, see if water comes out. Apparently there is a diaphram in that switch that will give you a problem. I had the same problem one day with mine. Eventually the light was flashing 4 times. If you look at the diagnostic notes that are on the cover plate, it talks about the problem being in some diaphram switch. I did the procedure to mine and got some water out of it. I reconnected the hose up, and have'nt had any more problems. I probably will replace that switch this year.. This same thing happened last year.

I'll have to try that tonite and get back to you....very interesting!

Do you have a pump hooked up to the drain line? If so, make sure that it is plugged in and working.

I checked the hose to the pressure switch and it seemed fine - no water came out. I also checked the pump. The resevoir was completely dry. I cleaned and re-lubricated and re-filled the resevoir and the pump came on. If the resevoir was dry, where should the water be coming from? There is a PVC pipe coming from the furnace to the pump but it was dry as well. I see a water line from the furnace which goes out the side of the house ( I think )
Any other suggestions?

One other thing I noticed: The flame sensor is in front of one of the burners and that burner tends to light slower than the others. At times, because that one doesn't light as quickly, the sensor will turn it all off, and then re-try again. When it tries 4 times and that burner still does not light soon enough, the furnace goes into lockdown. But sometimes it does light just fine so this is intermittant as well.

The water comes out of the by products of combustion as condensation. The pump is there to collect it and discharge the water. Sounds like time to call the HVAC guy.

Can you recommend any particular company to call for service?