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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3140
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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I have an armstrong air furnace (G2D95CT/U) furnace and Im

Customer Question

I have an armstrong air furnace (G2D95CT/U) furnace and I'm getting a 3 flash error code (low-fire pressure, rollout, drain pressure, or aux limit open). I've tried clearing my intake, exhaust, drain, pressure hoses and bypassing the pressure switches and haven't had any luck.
The furnace appears to turn on and run for about 2-3 minutes before shutting off.
Can anyone help?
Submitted: 11 months ago.
Category: HVAC
Expert:  Tim H. replied 11 months ago.

Tim H. :

Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Thanks for the opportunity to help!

Tim H. :

Hello there

Customer :

Hi

Tim H. :

Is that what that flash code indicates (above)?

Customer :

yes.

Tim H. :

First of all, you can't bypass the pressure switches. They are NO switches and close when inducer comes up to full speed.

Tim H. :

Is inducer motor working OK?

Customer :

it appears to be. everything sounds ok when it fires up.

Tim H. :

Have you tried taking the intake pipe OFF the furnace to see if it works this way?

Customer :

no. disconnect it from the inducer motor?

Tim H. :

The intake pipe is usually not glued onto the furnace and can be taken off easily to see if this helps. Another way is to take the upper door off. Accomplishes the same thing.

Tim H. :

As far as the flame rollout switch, do the burners light smoothly and shoot straight into the heat exchanger without wavering?

Customer :

everything seems glued. i have no idea how to check whether the burners are lighting.

Tim H. :

You can take the upper door off and easily see the burners. They may be behind a small window but can still be seen

Customer :

is the "upper door" the outside panel or the screwed on panel?

Tim H. :

The outside panel. Behind which are the burners

Customer :

actually i don't think they're lighting

Tim H. :

OK, they may not be lighting due to a plugged intake, exhaust, or a bad pressure switch

Customer :

i tried shop-vac'ing out the intake and exhaust and didn't get anything.

Tim H. :

OK, but these are PVC pipes that run quite a distance, correct?

Customer :

fair. 20 feet or so.

Tim H. :

So how do you know that something such as a leaf isn't stuck inside one or both the pipes?

Tim H. :

That's all it takes to cause that flash code

Customer :

i don't.

Customer :

is there a way to rule out the switch?

Tim H. :

That's why if you can take the intake pipe off the top of the furnace, and if it runs OK, that would help us find the problem

Tim H. :

Switches are hard to troubleshoot. They require a manometer and close as so may inches water column

Tim H. :

sorry, at

Customer :

i think i would need to remove the inducer. another question, i cleared the trap trying to trouble shoot. should i prime it again?

Tim H. :

No, no need to. The drainage on a high efficiency furnace can also create problems

Tim H. :

If it doesn't drain properly, water can backup and cause that flash code

Customer :

seems like everything is draining. and if it's not, it's dry now.

Customer :

so, i guess your best bet is exhaust?

Tim H. :

No intake pipe causes way more problems. Because it's sucking in.

Customer :

ok. i'll see if i can get it off.

Tim H. :

Of course, that's just ONE possibility. The code can be caused by many things. And it could even end up being a bad pressure switch.

Customer :

ok

Tim H. :

These kind of codes are perhaps the toughest to troubleshoot, unfortunately. Sometimes they even stump us PROS!

Tim H. :

You still there?

Customer :

yes

Customer :

still thinkin on it

Tim H. :

OK, I would recommend checking the pipes again, particularly the intake. If you can take it off the top of the furnace, that would help eliminate it as a possibility. Doublecheck all drain line connections, trap, and so forth. Make sure none of these are clogged. Check your pressure switches-make sure the tubing is on tight, not kinked. If all these check out, it could be a bad pressure switch. These are checked with a manometer, something you probably don't have.

Customer :

it appears to be blowing for about 2 mins, then the exhaust kicks in, then it clicks and shuts down...

Tim H. :

OK

Customer :

not sure if that means anything.

Tim H. :

Nope, it just means it doesn't get to the point of the pressure switch closing

Customer :

that's what i figured.

Tim H. :

Which could mean a plugged intake, exhaust, bad pressure switch, not draining. Same things I mentioned above

Tim H. :

Did you need any additonal help?

Customer :

i guess i may need to call in one of you pros. one last question, how would i tell if i had a drainage issue?

Tim H. :

You would typically hear a sloshing sound near the inducer when it starts up

Customer :

ok. well i'll keep troubleshooting and likely call someone in. thanks for the help.

Tim H. :

Yes, good luck! Thanks for using Just Answer and please don't forget to rate my service (bonuses are always appreciated). Feel free to post back with any additional questions. Have a great day!

Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3140
Experience: Experienced in all aspects of HVAC, both residential and commercial.
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