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Old 11-29-2009, 10:42 AM   #1
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Gas Valve test?


Does anyone know if there is a test or adjustment you can perform on honeywell gas valves. I have a lennox furnace with intermittent pilot. lately it has failed to light the odd time. When i go to check, the combustion fan is running but thats it. I turn off the power and gas valve and let it sit a few seconds turn it back on. if it doesnt light i rap on the side of the valve and it usually goes. Do i assume a faulty gas valve or is their test i can perform to be sure. Any ideas of the best/cheapest place to buy these?
thanks
dw

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Old 11-29-2009, 10:51 AM   #2
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Gas Valve test?


Measure voltage across, and current through, the valve.


Last edited by Yoyizit; 11-29-2009 at 10:54 AM.
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Old 11-29-2009, 10:54 AM   #3
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Gas Valve test?


how do you do that and what should they be at?
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Old 11-29-2009, 10:56 AM   #4
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Gas Valve test?


What is the model # of the furnace and gas valve? I am a Lennox tech. Rapping the valve is not a great idea as sometime it may stick open and become dangerous.
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Old 11-29-2009, 11:08 AM   #5
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Gas Valve test?


Lennox G26Q 3/4 -125-1

Gas Valve VR8204H 2801

THanks!!
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Old 11-29-2009, 11:13 AM   #6
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Gas Valve test?


Quote:
Originally Posted by trump View Post
how do you do that and what should they be at?
With a multimeter, and then compare the values to the specifications for the valve [which seem to be hard to come by].
A Websearch on your valve part number may turn up a test procedure.

If it's a 24vac valve I have a procedure and circuit for testing that your transformer is up to snuff. The parts for this test circuit may cost ~$10 or so, so if in doubt you may want to just swap out the 'frmr.

Last edited by Yoyizit; 11-29-2009 at 11:21 AM.
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Old 11-29-2009, 11:38 AM   #7
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Gas Valve test?


"so if in doubt you may want to just swap out the 'frmr."

Why not swap all the parts one at a time until you hit the right one? It should have a steady 24 volts to the valve.
Cozyparts.com for Lennox stuff.

Last edited by yuri; 11-29-2009 at 11:42 AM.
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Old 11-29-2009, 11:56 AM   #8
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Gas Valve test?


Quote:
Originally Posted by yuri View Post
"so if in doubt you may want to just swap out the 'frmr."

Why not swap all the parts one at a time until you hit the right one? It should have a steady 24 volts to the valve.
Cozyparts.com for Lennox stuff.
I should edit my posts more carefully.

I think there is value in reducing uncertainty no matter how cheap the part is, even if it means spending a few bucks and an hour or so making a resistor network. This becomes more true for HVAC people.

But, many DIYers would rather swap out inexpensive parts even if the likelihood of it being bad is low.
In a way, it makes sense. It may be a poor bet, but they don't have much money & time riding on the gamble.

When the DIYer wants more certainty is when the part is very costly and likelihood of it being the root cause is unknown. Like replacing a part or replacing the whole furnace.

If there is 24.0vac across the valve and it doesn't work right, it is almost certainly the valve. But since current is what moves the valve I'd rather have a current reading and a voltage reading.
If it's >24vac, an open valve? Probably, since frmrs don't get 'stronger' and they usually have poor voltage regulation. Could also be a rusty connection.
If it's <24vac, a partially shorted valve winding or a 'weak' 'frmr? Which one?

If the OP does do the measurements, which one of these 3 readings and 5 possibilities will he/she find? Place your bets.

Thanks for the parts link.

Last edited by Yoyizit; 11-29-2009 at 12:12 PM.
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Old 11-29-2009, 12:10 PM   #9
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Gas Valve test?


I have worked on thousands of furnaces and only had 1 weak transformer. They don't get weak as all there is in them is 2 windings of different size and insulation. Capacitors are another story. Sorry to disapoint you but there are NO values anywhere for resistance of gas valve coils etc etc. Nobody wants or needs them. Techs isolate the problem and change the part, period. The only spec we need are flame current, gas pressures etc. Our industry is not an electronic fixable one with Radio Shack parts and telling posters stuff that won't solve their problem only leaves them without heat longer, Sorry. There are also safety and liability issues and I don't tolerate advice which can compromise that. Circuit boards have critical flame failure circuitry and a DIYer with a soldering iron/static discharge etc can damage that and cause danger, period. I admire you wanting to help though.
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Old 11-29-2009, 12:23 PM   #10
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Gas Valve test?


Quote:
Originally Posted by yuri View Post
Sorry to disapoint you but there are NO values anywhere for resistance of gas valve coils etc etc. Nobody wants or needs them.
With all due respect, how does the factory electrically test the parts coming off the assembly line?


Lemme' ask you and Beenthere a question.

I sometimes do extreme skiing in Canada and PA.

Some people cheer
and some people hope I break my d@mn neck.

Which crowd would each of you be in?
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Old 11-29-2009, 12:38 PM   #11
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Gas Valve test?


Have no idea how they test them even if they do. My point is that not everything is on the net and searching for stuff that does not exist is futile. Hope you don't do a "Sonny Bono" someday. We need interesting characters or the site gets too boring and I move on.
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Old 11-29-2009, 03:49 PM   #12
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Gas Valve test?


Yoz.

With EXTREMELY FEW EXCEPTIONS(the child murderers on the news as of late, are those exceptions). I never wish harm to anyone.
So I would not be wishing to see you break your neck..
However, maybe falling on your butt would be something I might wish for though.

Kinda of like when I use to ride dirt bike. We always wanted to see one of us wipeout on a hill or jump. But never wanted anyone to get really hurt.
And seeing one of us get stuck in the mud boggs was always funny.

PS. Reading 24 volts across a valve, doesn't tell you if the valve is working or not.

Only tells you 24 volts is present.

Factory valve bench testing is easy. Input pressure on inlet side, Apply 24 volts, test for pressure on output side.
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Old 11-29-2009, 04:37 PM   #13
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Gas Valve test?


I would not recommend any diy to change out a gas valve. After the valve is in you must check for leaks, check the manifold pressure and also check temperature rise. That furnace I believe has a spark ignition and if it is the old johnson control it may not be operating correctly.
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Old 11-29-2009, 05:18 PM   #14
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Gas Valve test?


Don't I know you from somewhere?? Hvacmechanic.com?
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Old 11-29-2009, 05:31 PM   #15
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Gas Valve test?


That's what I was thinkin.

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