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 G20E Gas Valve Noise Intermittient
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7 Posts

Posted - 12/24/2011 :  10:32:36 PM  Show Profile  Reply with Quote
Lennox Furnace Gas Valve Buzzing Clicking Noise

The Furnace model is a G20RQ3XE-75-1, serial 5891G13125

A couple of weeks ago the gas valve started making a buzzing clicking noise. The noise sometimes last a few seconds then stops and at other times up to a minute and then stops. It might happen upon the next call for heat or not for several hours.

I monitored the voltage to the main valve and it is 24VAC when it is quiet and about 21-22VAC when it makes the clicking noise. I also checked the current to it and it draws about 130mA AC when it is quiet and working fine and about 110mA ac when it makes the buzzing clicking noise.

The ignition module was replaced about 10 years ago with a RobertShaw 780-715

I believe the gas valve is original; it’s a RobertShaw with the following numbers 7100 DER-S7C, 71F-11A-017, and 18G8801. I looked up a replacement and it seems to be a Honeywell 41K35 (VR8204H1048).

I was thinking that the gas valve is worn and almost ready to die, then I started to think that the output voltage from the ignition module being a little low is keeping the relay inside the Gas Valve from energizing but enough voltage for it to try, hence the clicking / buzzing.

Any thoughts or tests I can do?

Thanks and Happy Holidays

On another note, I noticed that the replacement gas valve 41k35 has the pilot tube connect to the top of it. One the current valve pat numbers 7100 DER-S7C, 71F-11A-017, and 18G880, the pilot tube enters the side?

Not sure if there is enough length to rebend the tube and get it to reach. I don’t have a 41l35 so I don’t know exactly how far the existing tube needs to reach. Comments?


32 Posts

Posted - 12/25/2011 :  07:00:35 AM  Show Profile  Reply with Quote
20 yrs old and the valve is worn and needs replacing. As tradesmen we carry a roll of 1/4 inch pilot tubing and make a longer line if necessary. Cozys may have it. U may have a bigger problem with the attachment to the pilot burner as it may have a longer special ferule. May want to call a Pro to do the job or order a pilot burner with it. It should be replaced anyway as they warp with age and develop poor flame signal problems.
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5983 Posts

Posted - 12/25/2011 :  07:04:07 AM  Show Profile  Reply with Quote
The next time you catch it buzzing and clicking, bypass the ignition control and run 24 VAC directly to the valve's main terminal. Never leave the furnace unattended while you are making this test. This will eliminate the possibility of the issue being related to the ignition control. Then you will have a firm answer. We only offer this step because sometimes it is very difficult to know the quality of the voltage with some volt meters when the power shuts off and back on very quickly.

As for the pilot tube, there is no notes from Lennox in the parts data on this model. Since most servicers would have a roll of pilot tubing and ferrules on their service truck, this is probably not something they would even take note of. If your in doubt, have some tubing and ferrules on hand when you change the valve., 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
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32 Posts

Posted - 12/25/2011 :  07:19:12 AM  Show Profile  Reply with Quote
95% certain U will need a longer line as it has to make a long U shaped loop and then drop back down to the top of the valve. May have to get the tube from a local HVAC shop or supplier. I get mine from/in a bag from Robertshaw.
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7 Posts

Posted - 12/25/2011 :  09:43:15 AM  Show Profile  Reply with Quote
Thanks for the responses

Updated Info

Last night I had the thermostat set to 63 degrees F (outside temp was about 43). The furnace didn't cycle as frequently maybe just once per hour. The clicking noise was never present. I had the ammeter connected inline and the valve would draw 160mA. Interesting how the valve would draw less current (120-130mA) when it is cycled more frequently, and 110mA when it would click.

Note: about the meter comment. The meter is an accurate Fluke 77 with a fresh battery. Also, when the main valve was clicking and the voltage measured around 21 - 22 VAC, I quickly measured the pilot valve voltage and measured a strong 24VAC

For the past couple of weeks I had it set around 66 at night and they furnace seemed to cylce every 10 -15 minutes. After hours of this the clicking would occur. Seems like the cycle frequency has something to do with the clicking? Maybe the ignition module main valves output voltage is slightly reduced when the module is warmer or is on a longer amount of time with short off periods.

Question about jumping 24VAC to the main valve when it occurs next. Do I leave the wire connected to the ignition module? Will backfeeding the module cause any problem? I'll need to be standing by and be quick to do this as the clicking only seems to occur at the start of the call for heat and then usually goes away after a few seconds.

Looking where the pilot burner screws into the valve how can I tell if it has a long special ferule? Looking at it installed the pilot tube is continuos and the threaded end goes straight into the valve with no visible adapter or ferule.

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192 Posts

Posted - 12/25/2011 :  10:55:06 AM  Show Profile  Reply with Quote
You may have a problem with low flame current at startup. That control uses a 2 stage system to prove. Has a lower microamps setpoint to prove the pilot ignition and then a bit higher to prove the main burner. The draft over the pilot will change with outdoor temp etc etc and can suck the flame away from the sensor to cause short cycling of the valve. I don't know those readings off the top of my head and they are board specific. In your case as a tech the first thing I would do and have worked on those units for 20 yrs and know them like the back of my hand and hate them is to replace the pilot burner and flame sensor. The pilot burner warps from heat and age and cleaning the sensor does not always solve the problem.At 10 yrs of age I run into problems with those burners but furnaces run a LOT in the Great White North where I am.
At 20 yrs of age and knowing all the problems which can occur I would buy a new furnace and that one is going to be a $$ pit for repairs and unreliable. Lots of them have cracked heat exchangers also.
Cut it twice and it is still too short. :":

Edited by - Baltar on 12/25/2011 10:59:22 AM
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7 Posts

Posted - 12/31/2011 :  10:30:32 PM  Show Profile  Reply with Quote

The gas valuve has still be making the noise off and on. It usually buzzes for around 30 seconds to a minute then stops. The furnace seems to continue to run.

As I posted before the MV voltage is around 21 - 22 VAC when the buzzing is happening and then once the buzzing stops its around 24VAC. This tells me that the 21 - 22 VAC is a little on the low side and not allowing the valve to open hard. 21 - 22VAC isn't enough voltage to open the valve hard but enough to get it to chatter and buzz.

I'd like to continue troubleshooting and see where I am getting the voltage drop. THe PV gets a full 24VAC.

Does anyone have a schematic of the furnace showing the path for the MV voltage that they can post or a link?

The wire to the MV comes straight from the Ignition Control Module. I don't know how the MV is derived in the control module. I am wondering if the problem is before the control module or the module itself?

Does anyone have a schematic of the control module?


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7 Posts

Posted - 12/31/2011 :  11:44:31 PM  Show Profile  Reply with Quote
I think I might have just fixed it!!!???

So I one by one removed every wire from the ignition control moudlue and I sprayed the connector with deoxit. Turned the furnace on and the buzzing was still there.

Then I wanted to jume (short) the MV to 24VAC as suggested earlier in the post to see if the buzzing would go away. I didn't have a wire at my fingertips so I turned my fluke dmm to the Current setting and shorted through my meter the PV adn MV, the buzzing went aaway. So now I am certain that the valve is not the problem, its the voltage to the main valve that is the pproblem.

So this is now how I think I fixed it. I went to measure the voltage to the main valve and turned the fluke to AC Volts from AC amps but forgot to move the test leads from A to V. So when I probed the MV to the MV/PV Common there was a very faint tiny spark ( I shorted the MV to common). The buzzing went away and now I measure 24.67VAC going to the MV. I think that shortng the MV momentariely burned off any oxidation in the MV voltage path. I would think that there are relays in the ignition module and now the MV Voltage is 24.7VAC, higher then ever before and no buzzing so far. Will see how it runs overnight.

One question that I had, the white sense wire, does that turn off the PV or MV or both?

Happy New Years!!!!!!

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32 Posts

Posted - 01/01/2012 :  07:48:54 AM  Show Profile  Reply with Quote
That valve is prone to developing an internal short between mv and pv and causing a huge bang/delayed ignition on startup. turns on the main valve while trying to light the pilot and before it is proved. they are also known to buzz and chatter when they get old. changed one a week ago. the white wire is the flame sensor. that valve can be very dangerous when it starts shorting internally so BEWARE.
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7 Posts

Posted - 01/01/2012 :  4:39:13 PM  Show Profile  Reply with Quote
thanks for the link

ran fine overnight and all day today. the furnace is installed in an old coat closet inside the home in the hallway near my bedroom.

I remeasured the PV and MV voltages and get 24.67VAC on both. In the past before I accidently shorted the MV to common, I got about 24.0 VAC for PV and MV. As I stated in my last post seems like shorting MV cleared up the problem. And I have nice healthy strong 24.67VAC now.

I just removed the wires from PV, PV/MV, and MV, I measure the resistance between PV adn MV and it measured infinity. I then measured MV to PV/MV and also got infinite, and then measured PV to PV/MV and got a few mega ohms. So the valve is not shorted internally.

Next to the furnace I saw the permit for the furnace installation. It was November 1992, so the furnace is going on 20 years old.

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7 Posts

Posted - 01/16/2012 :  10:15:58 PM  Show Profile  Reply with Quote
the buzzing sound is back

I took a few measurements and am getting a 3V drop across teh ignition module.

The ignition module was replaced about 10 years ago, the tech at the time put a RobertShaw 780-715 in, I guess that is what he had on the truck. I just ordered a lennox 30W33 ignition module.

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