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Furnace is not blowing hot air

Customer Question
Furnace is not blowing hot air
Submitted: 2 years ago.Category: HVAC
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Answered in 3 minutes by:
11/15/2015
HVAC Technician: Tim H., HVAC Professional replied 2 years ago
Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3,971
Experience: Experienced in all aspects of HVAC, both residential and commercial.
Verified

Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Please provide all information I request as it makes it more difficult to troubleshoot something when I'm not there onsite. Essentially, you become my eyes and ears. Thanks for the opportunity to help. At the end of our dialog, you will have a chance to rate my service, but please wait until we are finished and you're satisfied you have all the information you need.

I'm sorry to hear about your issues with your furnace. When the furnace shuts down, what LED flash code do you get?

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Also, can I get full model number? Lennox made two furnaces beginning with G40, the G40UH and the G40 DF.

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Customer reply replied 2 years ago
G40UH, I haven't seen any flashing lights on the circuit board
Customer reply replied 2 years ago
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Customer reply replied 2 years ago
I didn't know it was an additional charge for a phone call.. I just need help trying to troubleshoot the furnace.. It's blowing cold air when the thermostat is set to heat
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

OK, if it's blowing cold air, there will be a flash code in the small window in bottom of the furnace. I need that code.

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Customer reply replied 2 years ago
How will this code appear? With the furnace powered on? The furnace is on and circuit board cover is off and I don't see a light
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

It will not be seen in the top panel. It's in the bottom panel viewed through a small window. The code appears with furnace on, correct.

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Customer reply replied 2 years ago
Green and red flashing rapidly
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

OK, now I need you to count the number of green flashes followed by a pause and the number of red flashes followed by a pause.

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Customer reply replied 2 years ago
They are flashing at the same time at a rapid pace and I haven't seen a pause
Customer reply replied 2 years ago
Green light is just flashing now
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

If they are both flashing simultaneously at a fast rate, that's a call for heat. Is the inducer motor at the top of the furnace running?

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

How many green flashes followed by a pause?

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Customer reply replied 2 years ago
The green light is flashing at a half second pace continuously
Customer reply replied 2 years ago
When the light was flashing I counted up to 60 flashes and no pause
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

That means that the prove switch (pressure switch) was not made. Check for blocked vent or inducer not running. Also, pinched pressure switch hose or bad pressure switch.

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Customer reply replied 2 years ago
Green and red lights came back on flashing
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

First off: Is the inducer motor running?

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Customer reply replied 2 years ago
I'm not too sure what the inducer motor is
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

The inducer motor can be seen in Figure 1, page 14 of this manual.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Called combustion air inducer in the diagram.

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Customer reply replied 2 years ago
the black circle that spins? Combustion air inducter runs when the red and green lights are flashing
At the moment only the green light is flashing and inducer is not running
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

In that same diagram, they show a combustion air prove switch. It is round with a hose attached. Take the hose off, not on the prove switch end, but the other point it attaches and gently suck, then blow through the hose a few times.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

When you're done, put hose back on and try again.

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Customer reply replied 2 years ago
I don't see a hose
All I see are electrical wires
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Look for a small round part with a rubber hose attached.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Probably black in color and hose may be black, too.

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Customer reply replied 2 years ago
Ok I see it
Small round part (Honeywell) with two electrical wires and a red in color hose
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Yes, now need you to:

Take the hose off, not on the prove switch end, but the other point it attaches and gently suck, then blow through the hose a few times.

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Customer reply replied 2 years ago
Take the hose off the black small round piece?
Or on the opposite end that has the inducer spinning
Customer reply replied 2 years ago
the inducer is spinning now.. Should I power it down first?
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Nope, as I said, not on the prove switch end, but the other end. If you want, turn furnace off first.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

The prove switch is the small black round part.

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Customer reply replied 2 years ago
Just to be clear the prove switch is the small black piece with two wires coming out of it with the hose attached in the top right part of the furnance
Customer reply replied 2 years ago
this hose is only about 2 inches in length
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Yes. Leave the hose on that part, but take the other end off and gently suck then blow through the hose a few times. We are trying to "break free" the pressure or prove switch.

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Customer reply replied 2 years ago
I can take it off and blow in it but not real effective if I can't take the whole part off both ends
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Nope, wont' do any good if you take the other end off.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

If it's too short, you may need to go up to a hardware store and pick up a longer length of hose to perform this task.

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Customer reply replied 2 years ago
Anything else I can do?
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

If this doesn't work and inducer is running, the prove switch may be bad and would need replacement.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

We are trying to do something that will prevent you from having to buy a part and has worked for me many times.

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Customer reply replied 2 years ago
Ok
Customer reply replied 2 years ago
I can't seem to pull this hose off
Customer reply replied 2 years ago
I'll have to try and disassemble the price switch to get the hose off
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

If you need to perform this and get back to me later, that's fine. Sometimes the hose is hard to get off on the other end because it gets "welded on" due to the heat.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Why don't you go ahead and work on doing this, then post back when you get done. Otherwise, as I said, prove switch may be bad.

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Customer reply replied 2 years ago
Got it off! Blew in the hose
Customer reply replied 2 years ago
Now what
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Suck, then blow a few times. Gently. Then as I said previously, when you're done, replace hose, reset furnace (power off, then back on) and see if it starts.

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Customer reply replied 2 years ago
Ok will turn back on
Customer reply replied 2 years ago
Green and red flashing together again
Customer reply replied 2 years ago
Still blowing cold air
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Red LED off, green flashing slowly?

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Customer reply replied 2 years ago
red is out now and green is flashing
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

OK, more than likely this prove switch will need replacement. We tried anyways.

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Customer reply replied 2 years ago
Grrrr this sucks
Customer reply replied 2 years ago
No heat! Will have to continue to troubleshoot
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Yup. But at least now you have a better idea of what's going on.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

One other thing you can try: on the other end of the tubing on the inducer assembly, where pressure switch hose attaches, there is a small barb that hose pushes onto. Take a small drill bit and push in and ream this out, make sure its clear. Occasionally this will plug up with rust, debris. I'm not saying this will work, but worth a try.

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HVAC Technician: Tim H., HVAC Professional replied 2 years ago

Did you have additional questions on this? Otherwise, good luck! Thank you for using Just Answer and please don't forget to rate my service as that's how experts get paid (Thanks in advance for any bonus left). Otherwise experts work at their own time and expense. Feel free to post back with any additional questions.

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Customer reply replied 2 years ago
I had to call a tech out today..
HVAC Technician: Tim H., HVAC Professional replied 2 years ago

OK, I can understand your decision to call in a pro. Thanks for using Just Answer and please don't forget to rate my service.

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Tim H.
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