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Discussion Starter · #1 ·
Hello!
I have gone through a fair amount of options trying to solve this and it has not been fruitful. I was wondering if anyone on here might have experienced this before, or maybe has a recommendation on what I should try next?

We got a house last year with a Carrier furnace. We are in the pacific northwest, so there there is not AC in the home. It had a Honeywell smart thermostat installed. We tried to turn on the fan only (no heat) right after we moved in because it was summer/hot. It blew heat. I initially thought the thermostat was either faulty or wired incorrectly, and the lady wanted a different thermostat, so I replaced it with an Ecobee 4. The Ecobee and furnace have all 5 wires connected in the correct places, and the ecobee has heat/fan/cool settings. Even on the new thermostat, it doesn't matter if I have it on fan only, heat, or cool... it only blows heat.

Fast forward some research and time and I purchased a replacement control board for the furnace on ebay for fairly cheap. I replaced the control board for the furnace a couple of days ago, and then factory rebooted and reconfigured the thermostat. It still doesn't matter what setting it is on. It still only blows heat!

Make/Model: Carrier 58STX090-14
Gas furnace only. No AC attached.
Thermostat and furnace have all 5 wires attached.
I have replaced both the thermostat and the furnace control board.
No matter what setting it is on, it only blows heat. The problem remains.

Any ideas???

Thanks!
 

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Is your furnace and or ducts in a hot place? If yes, it will blow warm in continuous fan mode, especially during the first few minutes.

Can you take the cover of the furnace off and see if the burners are actually firing when you get heat?

Please do not replace parts without diagnosis.
 

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Discussion Starter · #3 ·
The furnace is definitely on and blowing heat. It is in a partial basement that normally doesn't get over 70, and it is for sure kicking on the heat.
 

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There may be a short in the thermostat wires or it's been mis-wired.

Set the stat to off, open the furnace and jumper R and G, only the fan should come on. You'll need to depress the door switch with the blower access panel removed to get it to work.
 
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