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Heil Furnace - Induction motor runs but taking long time for igniter to start

Heil Furnace - Induction motor runs but taking long time for igniter to start


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Old 11-16-15, 05:42 AM
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Heil Furnace - Induction motor runs but taking long time for igniter to start

Hi, thank you in advance for any assistance.
We have a 16 year old Heil Furnace.
Model NTG9075FGA3 / GNM075N14A3

Just this heating season (Wisconsin) we have begun to notice that the induction motor is running longer before the igniter will start to glow.

The thermostat calls for heat, the induction motor starts within seconds and then there is a delay in which the induction motor runs before the igniter will start to glow. It can be anywhere from 40 seconds to 3 minutes. Eventually the igniter will glow and the pilot will start followed nearly immediately by the main burners.

Once started, the furnace runs until the thermostat comes to temperature and calls for it to shut off.

Since the igniter does glow, and it starts, we don't think it is the igniter, pilot or flame sensor.

This furnace has a "smart" gas valve. Could it be the controller on the valve? A pressure switch or the main control circuit board.

Any suggestions on what order to start troubleshooting and any tests to run would be great. We are not technicians but are willing to try.

Thanks in advance.
Jean
 
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Old 11-16-15, 07:59 AM
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There is a sensor (pressure or vacuum) on the inducer exhaust that must be satisfied (closes electrical contact) before ignition can proceed. Make sure the hose connection from the inducer exhaust pipe is not loose, cracked or kinked. Once this sensor is satisfied, it appears the ignition goes to completion correctly.Hope this helps.
 
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Old 11-16-15, 09:46 AM
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There is a "designed in" delay between the starting of the draft inducer motor and the ignition system.... it's called pre-purge. It can be anywhere from 20-60 seconds depending on the control board.

I'm slightly confused here..... the service manual shows an intermittent ignition system.... spark lit pilot.... but you said "the igniter will glow" ???

hvac partners//docs/1011/Public/01/44003110501_ICP_1774.pdf


This is a 16 year old high efficiency condensing furnace. It should be regularly cleaned and serviced by a technician. Your gas provider should have a good service crew.
 
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Old 11-16-15, 10:17 AM
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Hi, thank you. I have checked the black rubber hose from the negative side of the pressure sensor/switch to the inducer motor and it appears fine - well seated, no cracks or kinks.

This latest time it took the furnace 4 min and 42 sec before it kicked in. It appears to be taking longer and longer each time.

Any additional insight is appreciated.
 
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Old 11-16-15, 10:22 AM
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Hi thank you. The link is to the exact manual for my furnace. On page 5, in the circle where it shows part 23, 24 and 25 - there is a small straight rod (I believe it is called a hot surface igniter). That "rod" starts to glow, which then causes the pilot to light, which then lights the burners. I am not sure if I am describing it the best. But the best I can put it is the induction motor runs for increasingly longer period of time before the ignition happens. Just now it took 4 min and 40 sections before the ignitition.

Hope this helps and thank you.

Jean
 
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Old 11-16-15, 10:34 AM
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Must be a variation of the spark ignition. No problem.... that's not where the problem is.

A common problem is a plugged connection where the rubber hose connects to the draft inducer blower. It's a little tiny hole. Remove the rubber hose and use a small drill bit or piece of wire to clean out the port.
 
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Old 11-16-15, 11:13 AM
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Hi - There is no bleed port for the induction motor. It is a molded black plastic outlet spout with no tiny hole (I have seen pictures of bleed ports on other posts). I removed the black rubber hose from the induction motor and from the pressure sensor. There was one drop of water in the hose at the motor end. I blew out the hose and reconnected it. Then started the furnace and it took 46 seconds.

Not sure if this "fixed" it or we also noticed that when we were troubleshooting, if it had just ran and we forced it to cycle again, it took much less time. Then after it sits for a hour or more it takes much longer (the 3-4 minutes).

I will keep monitoring and posting.

Any other thoughts?
Jean
 
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Old 11-16-15, 12:04 PM
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You are dealing with a minute bit of vacuum to activate the pressure switch. Anything, even a drop of water, can block that. On a condensing furnace you have condensate drain lines that must be cleaned and emptied.
 
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Old 11-16-15, 01:23 PM
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The next cycle time was 1 min 2 seconds - much better than before. I will have to look into and figure out how to clean out our condensing lines. Hopefully this will continue to work.

Thanks again
Jean
 
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Old 11-16-15, 03:49 PM
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The likely reason for the delay in ignition is that the pressure switch isn;t closing promptly after the inducer motor comes up to speed.

You should verify that, however. On one side of the pressure switch you should have 24 VAC whenever the inducer motor is on. The other side should have 24 VAC when the pressure switch closes, which ought to be when the inducer motor comes up to speed.

Check that and verify that the pressure switch isn't closing promptly, and when it does close the rest of the ignition sequence proceeds.
 
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Old 11-17-15, 10:10 AM
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Thank you. We will try testing it. We have never done that before. I have a multi meter and it has an A~ setting. What I do not understand is where to put the leads. I assume I put one on the side of the switch that I want to test, but where do I put the other lead - to the frame of the furnace, somewhere else?

I will do a you tube search for how to do this but if you have any quick instructions, that would be appreciated.

Also, would it be simpler to just replace the pressure switch?

Thanks,
Jean
 
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Old 11-17-15, 10:21 AM
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No... don't just change the pressure switch. They very rarely go bad.

There should be two wires on the pressure switch. You should put your meter on AC~ VOLTS.
(A~ is AC amperage and is a scale you will probably never use.)

Put one probe on each wire of the pressure switch. With the furnace idle but powered up..... there should be 24vac between the terminals. When the inducer starts running on a call for heat.... the voltage should drop to 0v and stay there.
 
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Old 11-18-15, 01:47 PM
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Sorry for the delay. Just figured out how to use the multi-meter. Now all I need is another set of hands to actually do the test Will post once I have the voltages.

The good new is the furnace still runs, the last time for the blower fan to kick in was 1 min 45 sec.

Thanks again,
Jean
 
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Old 11-22-15, 01:43 PM
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Hi -

I pulled off the hose to the pressure switch and put it back on and then did the voltage test on the pressure switch - It was 24v and then back to zero right away so it looks like the switch is good. When we did this the furnace fired right away.

We noticed some moisture and a fresh drop of water under the induction motor. We wiped it dry and will monitor it to see if any new water forms. If we get water, any idea where it is coming from and why we are getting it? We checked the drain hose and it was kinked but water could still pass through it. We did un-kink it.

Any suggestions?

Thanks Much,
Jean
 
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Old 11-22-15, 04:09 PM
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>


You have a condensing gas furnace which condenses the water vapor produced by burning gas back into water, recovering the latent heat of changing water from a gas to a liquid and cooling the combustion gasses down as well.

But the furnace needs to get rid of that water. It has a drain system to drain water away from the inducer motor out through a drain which may lead to a pump or other method to get rid of it.

Very likely that drain system is plugged up someplace. You need to inspect the whole drain system until you identify what is plugged up and correct the problem.

That could also include the PVC pipe that supply combustion air to the furnace and vent out combustion gasses as well. If one of those pipes sag or fail to drain, that can cause the pressure switch to stay open.

That you have water dripping from the inducer motor strongly suggests that you have a drainage problem and that the condensate is backing up into the inducer motor fan.
 
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Old 11-24-15, 05:25 PM
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Hello,
On our furnace, the back side of induction motor is mounted to part 15 on the diagram which is called the "transition assembly" At the bottom of the transition assembly is where the drain tubing is connected.

I pulled off the drain line from the trap and stuck my finger up into the connector. Quite of bit of water came out of it ~1-2 ounces. We then took off the induction motor and there was water inside the bottom of the induction motor. We then ran water through the open induction assembly and it freely flowed out of the drain tubing.

So, it appeared that water was collecting inside the induction motor and may not have drained out of the drain tubing. But that is free flowing now so it should resolve the problem.

We also took a shop vac to the exhaust pvc where it connects to the induction motor and it blew freely to the outside of the house - no clogs or animal nests.

Question - Is it normal to be getting condensation from the exhaust pvc pipe that condenses back down into the induction motor and then gets drained out through that port. It would appear to be designed that way and it seems to make sense since it is hot moist air that eventually will condense somewhere. Just want to double check.

I will continue to monitor the time it takes from the start of the induction motor to the start of the flame and let you know if this has solved our problem.

Thanks again for all of your input.
Jean
 
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Old 11-30-15, 03:56 PM
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I have been monitoring it. After the induction motor starts, it can take as short as 50 seconds or as long as 4 minutes for the flame to start. There is water dripping from the bottom of the induction motor housing. Can't figure out where the blockage is because we ran water through the assembly that the induction motor attaches to and it ran freely through the hose to the drain. Might be time to call a professional.

Any other suggestions are appreciated.

Thanks,
Jean
 
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Old 12-01-15, 12:40 PM
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The reason it is taking so long to ignite is probably because the pressure switch isn't closing.

After the thermostat calls for heat, the inducer motor should switch on. When the inducer moor comes up to speed, I should develop a negative pressure sufficient to cause the pressure switch to close.

When the pressure switch closes, THEN the rest of the ignition sequence can proceed.

Use an AC voltmeter to see f the pressure switch isn't closing.

>


Yes, it's normal.

>


Look some more. SOMETHING is preventing that water from draining out of the furnace!
 

Last edited by SeattlePioneer; 12-01-15 at 01:04 PM.
 

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