Thermal Zone Furnace Blower Fan Spontaneously Turns On


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Old 09-20-11, 06:39 PM
J
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Thermal Zone Furnace Blower Fan Spontaneously Turns On

So, about 6 weeks ago out of the blue, I hear and feel the air blowing out of my heat registers in my house.

I check the thermostat just to make sure the heat wasn't on - as I only have central heat/no AC. It was set to the off position, as I usually do in the summer months.

I check the furnace and there isn't any heat running, just the blower fan. I do notice from the inspection holes that some LED lights are blinking continuously. From the chart on the furnace access panel, I see that the continuous flashing LED light means there is a "False Flame/Gas Valve Relay Short" code.

So, I start to research online as to what may be causing this and came across a few recommendations to pull out and gently clean the flame sensor, which I did. I thought the problem was fixed, as over the past week, the blower fan only kicks on when the thermostat tells it to now and the heat comes on.

Tonight, however, the blower fan kicked through on a cycle and I see the same flashing LED lights again. I turn off the power to the furnace and start it back up and the LED lights are solid, meaning power is on. I turn up the thermostat and the furnace runs a normal cycle.

What could be causing the blower fan to turn on by itself with no heat. Any recommendations on what else to check for?

Model is GM072K12A

I'd hate to call an HVAC technician and be charged and arm and a leg for something I can do myself.

Thanks!
 
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Old 09-21-11, 02:37 PM
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It may be a bad control board.
 
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Old 09-21-11, 05:43 PM
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Is there a way to test the board prior to buying a replacement?
 
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Old 09-22-11, 04:46 PM
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I can not find a manual for your furnace online. You need to verify the LED fault code and definition.
 
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Old 09-28-11, 05:28 AM
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Ok, so I did a little bit of my own work on the furnace.

I re-cleaned the flame sensor and when I put it back in, I started to get two separate error codes.

Red LED: Contiunous Flash - False Flame/Gas Valve Relay Short
Yellow LED: Would flash on and off/Stay contiunously blinking - Low Flame Detected

So, I thought I had damaged the sensor in my attempt to clean it. I purchased a new one and replaced it. When I first turned the power back on to the unit, I got a solid red LED - POWER ON indicator and nothing else. I thought, PROBLEM SOLVED. However, maybe an hour or so later, I hear the blower fan running and cold air running through the vents. Now, I know my thermostat is off, but I re-check it to confirm, and it is. I go down to the furnace to check the fault codes and I get the following, again:

Red LED: Contiunous Flash - False Flame/Gas Valve Relay Short
Yellow LED: Would flash on and off/Stay contiunously blinking - Low Flame Detected

I have done my best checking voltages from various guides elsewhere on the internet and all readings seemed to be ok, although I can't say that I checked every possible thing there is to check, as I am new to this.

The only thing I can think is, that it was a very wet summer and I had some water issues in the basment - nothing, however, near the furnace. I was running a dehumidifier non-stop all summer to control the dampness. But, could the board have been damaged from any dampness in the air?

Replacing the board looks to be fairly easy, I am very proficient in repairing PCs and this just looks like a motherboard swap out, but any recommendations on what else to check prior to buying a ~$200 replacement board?
 
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Old 09-28-11, 04:28 PM
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IF you are sure that there is no flame when you get that code then I would replace the board.
 
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Old 09-28-11, 04:30 PM
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I am positive there is no flame. I am literally standing at the furnace as I flip the main power back on and stand there to watch it (last time I stood there for 30 minutes) and much like previous times, the fan kicks on and the LED flashes with the same fault code.

I will order the board this week and replace and will hopefully be posting the resolved issued.

Thanks for all your help!!
 
 

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