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Bill, HVAC Technician
Category: HVAC
Satisfied Customers: 318
Experience:  15+ years service tech.
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I have a Lennox G41uf. LED 1 and 2 are alternating SLOW Flashing

Customer Question

I have a Lennox G41uf. LED 1 and 2 are alternating SLOW Flashing error code. After turning off the power to the unit and starting it up again it heats the house up to temperature then goes into error code described above. While checking the unit it did enable the igniter 5 times and the gas was also burning 5 times. For about 5 seconds each time. It seems that the controller board is not telling the main blower to turn on so it shuts itself down. Powering down the device and powering it back on makes it heat the house every time (JUST ONCE) before entering the error code again. external venting was checked and is ok. Ignitor also works every time. Gas does come on every time. Filter is new and I also removed it to ensure easy air flow for testing. Where else should I check and is it the controller board?
Submitted: 7 years ago.
Category: HVAC
Expert:  Bill replied 7 years ago.
the alternating code you say , means an improper groung on the main power to furnace or input power is 75 volts or lower, the power outage you had goes inline with the fault codes
Customer: replied 7 years ago.

You are describing an alternating FAST flash not a SLOW flash. Which is WATCHGUARD - burners failed to ignite. Yet I have checked the burners and they do attempt to ignite 5 times successfully. Also when the system generates the error code the system does do a normal 1 hour reset and works after the auto reset.


Expert:  Bill replied 7 years ago.
ok now i see, try to unplug the connector for the combustion blower and plug it back in this code only describes a problem with the cumbustion blower motor....
Customer: replied 7 years ago.

I had already tried that by checking all wires. This system is installed in a 2 year old home. So the system is fairly new. So wires are not an issue here. From my original post I also mentioned that the conbustion motor was working. Even on the 5 attempts the controller makes the combustion motor kicks in fine and so does the igniter and gas. The system after the 1 hour reset just finished being on for about 30 minutes heating up the house. I just verified it and there is no error code. But what happens is when it attemps to kick in again I get the error code again. Then the system reset after another hour and runs only once again to heat up the house. Then again the error code and the clyle starts all over again.


Expert:  Bill replied 7 years ago.

ok , i know this is a newer system, but the diagnostics of these new systems ar rarely wrong, i have seen electrical arcing on the small connector ends of the combustion blower just remove and inspect them than replace.

let me know if you want me to op out so others may answer....

Customer: replied 7 years ago.
Hi, I've done as you said and unpluged the wires. They were a firm fit. You do understand that the system does work when you power the unit off and back on again. It's only after the system has fired up and shut down once completely that the error code appears. The last time the system was on for 30 minutes. How that I had to shut down the system again it will take it some time to get the error code again as the system always works fine after a reboot. I you feel you need to opt out thats fine. More heads may be better. Its up to you.
Expert:  Bill replied 7 years ago.

ok, i have one last thing, above the comb motor assmbly there is a black pressure switch this switch is used to verify comb motor operation, sometimes if there is enough slack in the small air tube it will trap moisture and not work each time, after a heating cycle remove this tube and blow it out than reattach if the furnace lights at next cycle this could be the issue....

Customer: replied 7 years ago.
No Luck - the hose was pretty dry and clean. Its 1am here, got to work tomrrow. The controller boards in these systems are not electrically surg protected. I"m guessing the conttroller chip onboard lost its marbles. Got to call it a night. Your web site is generating errors now on my replys.
Expert:  Bill replied 7 years ago.
must be the board all other things have checked out , good night
Customer: replied 7 years ago.
I live in Mississauga Canada (L5N 8M7)- from whom can I call to purchase a new board and what is a good asking price for the board?
Expert:  Bill replied 7 years ago.
in the states you must go to a lennox dealer, i think it would work the same for canada..
Customer: replied 7 years ago.

Can you give me an estimate on the price of this board in US funds please?