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-   -   Goodman Furnace GMNT100-4b Won't stay on (http://www.diychatroom.com/f17/goodman-furnace-gmnt100-4b-wont-stay-30912/)

freeslporer 10-30-2008 10:27 AM

Goodman Furnace GMNT100-4b Won't stay on
 
Hello, maybe someone can help me. I have a 4 year old Goodman Furnace GMNT-100 4b
Here is exactly what happens. The Stat asks for heat the inducer blower turns on, the igniter turns on , the gas valve opens and the flame turns on, then the fan turns on. I get heat for around 4 min… then the fan turns off, but the flame stays on , tripping the over limit switch. I get 4 flashes on the LED board. The flame turns off, no heat, a minute later the fan goes back on cools down the unit, the LED goes back to solid red, and the whole thing starts again? I cleaned the Flame sensor, I have a new filter, there are no blocked registers or returns. I took off the stat and jumped the red and white wire…. Same issue.
ALSO the fan setting is set to auto. If I set the fan to ON with heat off the fan stays on Indefinitely, if I set the Fan to ON and then turn the heat up… the fan will start acting like above… After the unit cools off the fan will run in ON mode again, but only if no heat is requested.
Thanks

dac122 10-30-2008 11:55 AM

Any blockage in your exhaust pipe? Others here might have a way for you to measure your temperature rise to see if its in spec.

What's the warranty on that baby?

freeslporer 10-30-2008 01:20 PM

Quote:

Originally Posted by dac122 (Post 178720)
Any blockage in your exhaust pipe? Others here might have a way for you to measure your temperature rise to see if its in spec.

What's the warranty on that baby?


The exhaust pipe is at eye level outside my home on the side. I blows pretty strong.

The UNit was built in 6/04 so its good till 6/09 5 year on parts I am not the original owner so this is what Goodman told me based on Serial #.

CAn it be something with a fan relay or a circuit board?

SD515 10-30-2008 06:42 PM

This is an odd problem. I slightly suspect a bad/loose wire connection somewhere, but more likely a board problem. Just odd that if it's a fan relay, why it does it during heat mode and not all the time (fan ON/no heat). Long story short...I would be suspicious of the board...the chip sets that control the furnaces functions in particular.


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