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 Repairing and Servicing Lennox Products
 Repairing / Servicing Lennox Gas Furnaces
 G20 loud clicking before lighting
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bwaindwain

3 Posts

Posted - 12/03/2010 :  8:50:39 PM  Show Profile  Reply with Quote
I have a Lennox G20Q3/4E-100H-3 natural gas furnace in my 17yr old house (I've only owned the house for 2 yrs). My furnace seems to work fine but it makes a loud clicking before it starts blowing heat. I can hear the clicking through the whole house. I took the cover off and watched it start. Here's what happens when the thermostat calls for heat:

1 very faint clicking sound, very fast (4 per second)
2 pilot (small flame) lights immediately
3 continues with faint clicking for about 30sec
4 loud, slower clicking starts (4 to 8 times, about 1 per sec, uneven)
5 burners light
6 blower starts

I'm concerned about the loud clicking #4. I can hear it throughout the whole house. Everytime it starts it's a different number of clicks. It comes from something higher up in the furnace above the burner, not sure where. It sounds like a solenoid opening & closing, except the last time (just before the burners light) it doesn't close (?). Any idea what it is? Should I be concerned?

Cozy.Support

5851 Posts

Posted - 12/03/2010 :  9:41:48 PM  Show Profile  Reply with Quote
Clean or replace the flame sensor. If the pilot light is small and not engulfing the flame sensor in a the blue mantle of the pilot flame, you may need to clean the pilot orifice or adjust the pilot flame. If you still have the issue, you may have issues with the ignition control, but it would be best to find someone to measure the flame current for you if you do the above and still have issues.



CozyParts.com, Inc. is an Independent Lennox Dealer providing a national parts distribution resource for Lennox parts since 2002. The Cozy.Support team does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx
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slctech

2086 Posts

Posted - 12/04/2010 :  09:10:35 AM  Show Profile  Reply with Quote
As Cozy stated, possibly the sound of the spark ignition module generating the spark to the pilot assembly.

If your confident the clicking noise is not coming from the pilot assembly and is higher up in the system, will need to try and pin point the noise.

Is there any accessory items on your system such as a humidifier, electronic air cleaner, uv lights, etc?

Will need to investigate more.




I am not an employee of CozyParts, I generously donate my time. The services here are free, with honest intention to assist, however, this site is not free to maintain. Please make the effort if you need a part or tool to purchase from CozyParts.com. This will ensure this wonderful forum remains for years to come!! As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!
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MechAcc

1499 Posts

Posted - 12/04/2010 :  09:18:15 AM  Show Profile  Reply with Quote
Make sure that the ignition cable where it passes through the burner box is not dried out as well as the insulating grommet. This will allow the spark to short to case.

I am not an employee of CozyParts. The opinions that I post are my own.

Please have your furnace inspected annually by a qualified service technician. Have all of your fossil fuel appliances tested annually for carbon monoxide production by a professional.

Get a good Carbon Monoxide Alarm. Replace it according to manufacturers recommendations usually every 3-5 years. CO concerns are not just for the winter but 24-7. UL approved alarms alarm high. For a low level alarm do a search for CO Experts or NSI 3000 a low level CO monitor.
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bwaindwain

3 Posts

Posted - 12/04/2010 :  3:50:22 PM  Show Profile  Reply with Quote
Hey, thanks everyone for your help. This is great!

I took off the cover and cleaned the flame sensor with a five dollar bill (I'm in Canada, don't have ones anymore). It's hard to reach in there but I managed. Was I supposed to take it out and clean it?

I checked the cables & grommets and they're OK.

The pilot light is blue and about 1.5 inches high.

I don't have any accessories on my furnace (humidifier, electronic air cleaner, uv lights)

It starts up much faster now. The igniter stops clicking right after the pilot lights. There's still a few loud clicks but not as many. If it's still warm then there's only one loud click. It seems to come from either the light brown Honeywell valve thing on the gas pipe or the white rectangle box with wires up and to the right. See image below, area circled in yellow.



Thanks again for all your help and advice.
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slctech

2086 Posts

Posted - 12/04/2010 :  6:05:53 PM  Show Profile  Reply with Quote
Chance are the gas valve is chattering for some reason. Doubt any loud mechanical or clicking noise would originate for the "rectangular" box..the ignition control module. Does the noise from the gas valve coincide with the lighting of the main burners? Also could be the pilot solenoid side of the gas valve opening and shutting a few times. This happens due to different reasons, poor flame sense, dirty pilot assembly, poor grounding of either pilot assembly, burners, or ignition module, or a failing module.



I am not an employee of CozyParts, I generously donate my time. The services here are free, with honest intention to assist, however, this site is not free to maintain. Please make the effort if you need a part or tool to purchase from CozyParts.com. This will ensure this wonderful forum remains for years to come!! As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!
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bwaindwain

3 Posts

Posted - 12/05/2010 :  2:36:08 PM  Show Profile  Reply with Quote
The main burners don't start until the loud clicks stop. Yes, the clicks sound like a solenoid opening and closing something.

Seems like the furnace is back to it's old ways. Today it's been clicking a lot.
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slctech

2086 Posts

Posted - 12/05/2010 :  6:42:17 PM  Show Profile  Reply with Quote
I have seen this numerous times and is very difficult to properly diagnos the exact culprit. Basically, under normal operation the ignition module will simultaneously power the pilot solenoid and start spark operation to generate the pilot light. The pilot light energizes the flame sensor which in turns tells the ignition module the pilot has properly ignited and energizes the main solenoid of the valve to utilize the proven pilot to ignite the burners.
Now for any one of numerous reasons the ignition module is attempting to ignite the pilot over and over again ans finally the main burner ignites and things settle down. So what you are hearing is a hiccup in the pilot ignition or proving side of things.
Need a meter able to measure micro-amps and understanding of the sequence of ignition operation to really focus in on the issue. It may be as simple as a dirty pilot and flame sense assembly, grounding issues with the pilot assembly and/or ignition module, faulty ignition module, or faulty gas valve.
It would be prudent to measure the incoming gas pressure or clock the system to make sure that the inlet gas pressure is not in excess of manufacture ratings. High inlet pressure can cause either the pilot solenoid, main solenoid, or both to operate erratically.




I am not an employee of CozyParts, I generously donate my time. The services here are free, with honest intention to assist, however, this site is not free to maintain. Please make the effort if you need a part or tool to purchase from CozyParts.com. This will ensure this wonderful forum remains for years to come!! As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!
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