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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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My ducane furnace,inducer comes on, it lights, blower comes

Customer Question

my ducane furnace,inducer comes on, it lights, blower comes on. then shuts off after a few minutes. then inducer comes on after a bit but it doesn't stay on long enough to light. seems if I shut off the power, it goes thru cycle again but shots off again.
JA: Did you check the furnace's filters?
Customer: it was pretty dirty so I pulled it. don't have another to stick in
JA: Do you plan on doing the work yourself?
Customer: if possible. I am not a furnace expert by any means but I am a mechanic and can work on just about anything with something to guide me
JA: Anything else we should know to help you best?
Customer: i cleaned the flame sensor
Submitted: 5 months ago.
Category: HVAC
Expert:  D.E. Anderson replied 5 months ago.

Hi, how are you? Is there a circuit board in the blower compartment of the furnace? Thanks

Customer: replied 5 months ago.
Customer: replied 5 months ago.
pressure switch open with the inducer on is the code its flashing
Customer: replied 5 months ago.
as soon as the fan comes on, the flame goes out
Expert:  D.E. Anderson replied 5 months ago.

You mean as soon as the main blower starts up?

Customer: replied 5 months ago.
when the main blower starts the flame goes out
Expert:  D.E. Anderson replied 5 months ago.

Do you see the flames blow out any at all before the pressure switch error occurs and the furnace shuts down? Like do you see the flame pattern change?

Customer: replied 5 months ago.
let me look. if it will even start. after it does it once it takes a while to start up again. the inducer will come on for a few secs then just shot off
Expert:  D.E. Anderson replied 5 months ago.

Alright, is it tripping an error when the inducer shuts off without firing the furnace?

Customer: replied 5 months ago.
this time it wouldn't even fire the furnace. just started the inducer for 5 or 10 secs
Expert:  D.E. Anderson replied 5 months ago.

That's unusual. With no error code?

Customer: replied 5 months ago.
the error code is coming up right away. its 3 blinks. panel says pressure switch open with inducer on
Expert:  D.E. Anderson replied 5 months ago.

Is the draft inducer hot to the touch?

Customer: replied 5 months ago.
no, it is not
Customer: replied 5 months ago.
i just jumpered past the switch and the furnace came right on and the code is gone
Expert:  D.E. Anderson replied 5 months ago.

Flame pattern looks normal?

Expert:  D.E. Anderson replied 5 months ago.

Usually they will run longer than five seconds before tripping the error. Check the tubing running to the switch for clogs and such. Also check the connections the tube attaches to.

Customer: replied 5 months ago.
did that already
Customer: replied 5 months ago.
flame pattern looks normal to me i guess. blue flames blowing into the tubes
Expert:  D.E. Anderson replied 5 months ago.

Then I would replace the pressure switch, but I find it odd for it to act up when the blower starts up. The blower should not affect the function of the pressure switch. That makes me suspect a leakage in the heat exchanger, but your described flame pattern disagrees with that too.

Customer: replied 5 months ago.
none of the tubing anywhere seems to be clogged. i have a manometer. but not sure what the dp is supposed to be
Expert:  D.E. Anderson replied 5 months ago.

Often the labels will tell the amount of vacuum it should be. The labels on the switch. Seems the switch is defective. No change in operation now even when the blower is running?

Customer: replied 5 months ago.
label on the switch says .6" water column
my manometer is reading 1.5"
Expert:  D.E. Anderson replied 5 months ago.

You have a reading of 1.5" positive pressure?

Expert:  D.E. Anderson replied 5 months ago.

You would need at least .5" to trip the switch. So I would suspect a damaged draft inducer wheel, a clogged flue pipe, or a crack in the heat exchanger.

Customer: replied 5 months ago.
i am not sure which is positive or negative pressure. pressure from the flame box is .2 and from the inducer is 1.5 now. so that's 1.3"
Expert:  D.E. Anderson replied 5 months ago.

Disconnect the pressure switch tubing from the switch and hook that up to your manometer and tell me what the reading is. Just jump the switch to get it to run long enough to get a stable reading.

Customer: replied 5 months ago.
1.3
Expert:  D.E. Anderson replied 5 months ago.

That's too high. Either theres a blockage in the exhaust vent, there is a leakage in the system on the vacuum side such as the housing or heat exchanger, or there is an issue with the blower wheel.

Customer: replied 5 months ago.
ok. will it hurt to run that way over night to keep the house warm?
Expert:  D.E. Anderson replied 5 months ago.

Do you have carbon monoxide detectors in your home?

Customer: replied 5 months ago.
i do
Expert:  D.E. Anderson replied 5 months ago.

Yes, I think you will be fine. I just would make sure they are working so that we know you will be safe. My biggest fear would be if there is a small crack in the heat exchanger and flue gas leaking into the home.

Customer: replied 5 months ago.
exhaust vent seems to be fine. i don't know how it could have blockage
Customer: replied 5 months ago.
the blower does sound a little funny when it starts running. but the exhaust outside the house feels pretty strong
Expert:  D.E. Anderson replied 5 months ago.

Birds. Ice or snow if there is a lot of drift in your area.

Expert:  D.E. Anderson replied 5 months ago.

Oh well if it feels good outside then I doubt theres a restriction in the pipe itself.

Expert:  D.E. Anderson replied 5 months ago.

Maybe the wheel is missing a few teeth and it is just enough to prevent it from pulling the vacuum. does the wheel sound like it is imbalanced when it starts up?

Expert:  D.E. Anderson replied 5 months ago.

You can always pull the housing and inspect it. When you put it back on, use high temp silicone and just run a good bead around the housing where the gasket is. Works great to reseal it.

Customer: replied 5 months ago.
ok
Expert:  D.E. Anderson replied 5 months ago.

Please keep me updated with what you find. Do you have any other questions?

Customer: replied 5 months ago.
one other thing i just discovered. theres a vent on top of the flame box. and a rubber piece sitting on the furnace that fits down it it perfectly. this rubber piece reduces the vent from about 2" down to .75". When i put it in the manometer reads only .1"
Expert:  D.E. Anderson replied 5 months ago.

Is this a 90% furnace or an 80%?

Expert:  D.E. Anderson replied 5 months ago.

Must be a 90%. I never asked. One more idea. Check all of your drains and make sure the furnace is draining properly. I apologize for not asking before now. That was an oversight.

Customer: replied 5 months ago.
i don't see anywhere it says, but based on the btu in and out, it would appear to be 93% efficient
Expert:  D.E. Anderson replied 5 months ago.

If you have a PVC flue pipe it is. There is no reason to reduce the exhaust vent. If it is 2" that is fine. Check all of your drains. Make sure the draft inducer isn't holding water. Which would also explain the pressure switch issues.

Customer: replied 5 months ago.
i checked the drain before and i wasn't sure it was but i tried to straighten all the tubing and it for sure should be now. it has one of those pumps that it pumps the drainage across the room to the laundry sink
Expert:  D.E. Anderson replied 5 months ago.

Is there any kind of gurgling when the draft inducer starts up?

Customer: replied 5 months ago.
there is
Expert:  D.E. Anderson replied 5 months ago.

Remove the drain trap if you can from the furnace, have a bucket ready and see if you get any water flow out of it. You may have a clog in the trap, or the pipe that runs from the trap to the condensate pump.

Customer: replied 5 months ago.
the flue pipe is pvc
Expert:  D.E. Anderson replied 5 months ago.

Let me know what you find out with the drain.

Customer: replied 5 months ago.
i had done that previously. after it has been running for a bit i just shut it off and on and there was no gurgling anymore
Expert:  D.E. Anderson replied 5 months ago.

Ah, I see.

Customer: replied 5 months ago.
but i still have the 1.3" wc problem
Expert:  D.E. Anderson replied 5 months ago.

Then I would continue with the plan to pull and inspect the draft inducer.

Customer: replied 5 months ago.
ok. i will do that. probably in the morning
Expert:  D.E. Anderson replied 5 months ago.

Alright, keep me updated. Thanks

Customer: replied 5 months ago.
thank you
Expert:  D.E. Anderson replied 5 months ago.

Thanks