I am having the following issues with my forced air gas furnace. It has a White Rodgers 50A55-843 board. The valve has "36E03 205" on it, along with a logo which looks like a "C" with an "A" inside of it.

The majority of the time the furnace works. However some days in the morning I wake up and the furance is shut down. I got a blink code, but I'm not sure if it is either a "1" or a "Continuos Flash" blink code. Per the legend on the board, that means either "1: System Lockout" or "Continuos Flash: Flame sensed, 5 seconds without gas valve." Anyone know how to tell the difference?

What I think is going on is that the basement gets cold, causing a loss of pressure at the gas valve.

While testing it when it goes off in the morning, the forced draft motor starts, then the ignitor glows, then I hear a click at the board, followed by a 1 second pause, then a softer click, then an approximate 3 second pause, then one last click. The furnace will cycle like this 3 times before shutting off with the blink code described above.

This morning I warmed the pipes going into the valve by just wrapping my hand around them. They were noticeably cold, and after about five minutes of "warming" the furnace is now lit and blowing hot air. I opened up the basement vent, and hopefully that will solve the problem. I had a technician come out a couple weeks ago and he said everything looked fine, replaced the air filter, and gave me a bill for $70.00.

While testing, I also noticed a brown spot on the back of the control board. I replaced the control board last year due to a dark spot, but now I'm thinking it was a pressure issue all along. Are brown spots on the back of control boards a normal occurrence? It is not mounted, just hanging on the side supported by wires.

Could it also be the flame sensor? I have 4 wires going into the heat exchanger. 3 wires go to the board, and 1 goes to the valve. The 3 that go to the board are black and white and yellow. I believe black and white are for the ignitor and yellow is for the flame sensor. The wire that goes to the valve is shiny and ductile, almost like solder. Are flame sensor's intermittent? If so, what is the proper way to get a voltage reading? Strip the wire and hook up a multimeter, then splice and tape?

Thanks for looking. Any advice would help. I am contacting the technician again to look at the flame sensor and take a gas pressure reading into the valve, and also clean out the blower and look at the evaporator coil. However if his estimate is high, or if I think he is not taking a serious look at the problem like the last time I wouldn't mind doing it myself.

Is this natural gas or propane?

It's natural gas. The furnace is off again this morning. I am by the great lakes region of the northeastern part of the US, and we just had a warm front followed by a cold front. The basement seems warm, and the natural gas is working on my stove, and I'm getting the same blink code.

I called up the owner of the HVAC company who sent the tech out here. He pointed out that there should be another flue for the forced draft motor going to the outside, and the technician who performed the original work put the wrong filter in the furnace. Does that have anything to do with the problem I'm seeing, which looks flame sensor or gas pressure related?

Thanks.

work put the wrong filter in the furnance

Should not make a difference with the problem you are having.

He pointed out that there should be another flue for the forced draft motor going to the outside

Usually the are 2 plastic PVC pipes intake and exhaust of the 90+ furnaces but as long as the exhaust is going outside all should be OK.

Try cleaning the flame sensor with steel wool,Scotch Pad or sandpaper. Easy di=oes it if located around the ignitor since they break easy. Do not touch ignitor with your fingers. What is the exact brand and model of your furnace?