# Motherboard Advice



## JCG (Jan 28, 2021)

Hi,
Looking for some advice/help with a furnace issue. Furnace is a Guardline, model number GG9S080B12MP11A
The problem I am having is that even though the thermostat is set to 70 degrees, the house temp is dropping to 67, usually overnight. When we notice the house temp has dropped, I power cycle the furnace and it immediately kicks in and starts blowing heat.
A few years ago I was having a similar issue so I checked for an error code and found one, I believe it was a "high temp" error code. I called in an HVAC guy who said my furnace was probably too large for the house and was not getting enough cold air returned to the unit, causing it to overheat. He basically cut in a few wall vents to allow more air to get into the small room where the furnace sits. I have not had the problem since they did that, but I also do not drop my house temp to 65 degrees when gone like I used to. Trying to get the house to return to 70 from 65 is when the problem would arise.
That kind of made sense to me, but this year I am using my outdoor wood boiler to heat my house. If you are not familiar, the boiler outside burns wood to heat water to 186 degrees, that water is then pumped into my house and into a plenum or heat exchanger that resides inside the existing furnace, the furnace fan then blows air through the plenum and heats the house through the same ductwork the LP system uses.
This most recent time the problem occurred, I checked for an error code and there isn’t one, slow steady green light which I believe means waiting for the thermostat to call for heat. A power cycle got it running again.
What this is telling me is 1) There is nothing wrong with the thermostat, it is calling for heat but the furnace is processing that call correctly and 2) this is not related to my previous “over heating” error since there is no LP combustion taking place in the furnace (and no error code)
My thought is to replace the motherboard, it is easy to get to, and is about $130 so not too bad. If replacing the motherboard solves the problem, I will have saved myself some money over having a service tech do the work.
My concern is that replacing the motherboard is just a guess, I have no experience in this field and don’t want to waste my time and money.
Looking for professional opinions to help me choose whether I should try replacing the motherboard, or just call someone who is trained on how to diagnose the problem.
Thanks!


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## JCG (Jan 28, 2021)

Meant to say: 1) There is nothing wrong with the thermostat, it is calling for heat but the furnace is _NOT_ processing that call correctly


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