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My 1 year old furnace refuses to operate. Both the red and…

Customer Question
My 1 year old...

My 1 year old furnace refuses to operate. Both the red and green LEDs are on solid and the yellow LED flashes 3 times. No power to the thermostat.

Contractor's Assistant: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?

I have tried 3 different thermostats with no power showing to any of them Thought it may be the power supply since I replaced the 5A fuse.

Contractor's Assistant: Do you plan on doing the work yourself?

If it is not too complicated.

Contractor's Assistant: Anything else we should know to help you best?

I put a new fuse in but do not know how to test for 24V power

Submitted: 3 months ago.Category: HVAC
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Answered in 3 minutes by:
3/26/2018
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago
Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 1,024
Experience: I have been an HVAC/R mechanic/technician for 30+ years.
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Hi, I'm Brian and I'll be happy to help with this.

Since you have lights on the furnace control board, the problem is not with the 24 volt supply. It's more likely a safety switch of some sort has tripped. If your furnace has a drain switch and the drain is plugged that may cause it. If you can give me the make and model number of your furnace, I can look up the fault code and give better information.

Thanks,

Brian

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Customer reply replied 3 months ago
It is a Ducane 95G2E. I will check the drain, but guess that the problem is electrical. I was replacing the thermostat and may have shorted something out. It was not working well before that, but I thought it was just my Nest thermostat so I was going to replace it with a Honeywell. Now it won't turn on with either. The Nest says that there is no power to the 24V supply.
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

Ah, you may have incidentally popped the 3 amp fuse on the furnace control board. It's a plastic fuse that is the same type used in cars. It should be purple or sometimes it's a 5 amp yellow one. It's located on the furnace control board itself behind the blower panel.

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Customer reply replied 3 months ago
That was my first guess. I replaced the fuse, but still no response. The new fuse seems to be holding.
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

What lights are on the furnace control board after replacing the fuse again?

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Customer reply replied 3 months ago
Same as before; the green and red stay on solid. The yellow one flashes 3 times then goes out. The fan starts to cycle but then goes off.
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

When you say the fan starts to cycle, do you mean the combustion inducer fan or do you mean the main system blower?

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Customer reply replied 3 months ago
I believe it is the blower fan.
Customer reply replied 3 months ago
No, I tried it again and it is the combustion inducer
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

Ok, the red led is the fault led, the green shows status of heat and the yellow (amber) one shows how much airflow is being called to run from the main blower. If there is a fault, it should show up as a blinking red led. Both red and green on solid indicates normal operation on high heat. After the combustion blower shuts off, does the red led blink a code or do the leds all go out or if other, please explain.

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Customer reply replied 3 months ago
The red and green stay on steady. The yellow goes out. The panel on the door indicates the red and green should stay lit. It does not say anything about the yellow.
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

I must have the wrong manual for your furnace then. Can you confirm the entire model number of your furnace? It should be something like 95G2UH110... etc or similar

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Customer reply replied 3 months ago
It is a 95G2UH070BV12-60
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

Thank you for that, it will allow me to be sure I'm on the same page as you!

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HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

Ok I do have the right manual and the codes are still the same as the other one I was looking at. If the red and green led are on, the furnace should fire and stay on until the heat demand is satisfied at which time the green led goes out and the red stays lit (red should always be lit unless there is a problem then it's either out or it flashes). If the furnace doesn't fire, either the demand has been removed, red led on green off (heat no longer called for by thermostat) or there is a problem in the ignition sequence, at which point the red led should flash a fault code.

The yellow led is just an indication of the amount of airflow the main blower should deliver and any flashes indicate normal operation.

I don't understand why your thermostat would appear to have no power when the leds on the furnace indicate power is on and there is a call for heat (green led lit). There is a gremlin somewhere that's for sure.

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Customer reply replied 3 months ago
Thanks for your efforts on my issue. I do believe that I will call in an exterminator (technician) to deal with the gremlin after all.Earl
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

I wish I could have been of more service to you Earl. Thanks for using Just Answer. Best of luck to you sir.

Thanks,

Brian

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Customer reply replied 3 months ago
No problem. It was worth a try. Best of luck
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 3 months ago

Thanks much,

Brian

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