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Old 01-29-2009, 07:58 PM   #1
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How to check gas control valve?


New project I'm having to work on at work. I have a greenhouse furnace (Modine, nat gas, 105 btu, 1986) that lights the burners intermittently. It has a standing pilot which works fine. Sometimes the burners light when called for heat, sometimes they don't. Right now, they don't. The control valve is Honeywell, no ID# on it. It has 6-8 wires, can't remember tonight but will look later. Try to get a photo if it will help.
Any suggestions for what to troubleshoot?
After reading some of the posts, I will try to listen for the valve to open. I can hear something click sometimes when I turn up the stat, but I am standing about 40 feet away. Will have to get someone to turn it up while I stand beside it to listen. Anywhere to check with a VOM?
I have checked with a local supplier who tells me that a replacement unit is not available but MIGHT be able to get a universal unit to fit.

I don't mind having to work on this as it is something else to learn about, but why does my job description say "laborer?"

Thanks for all help.
Richard

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Old 01-29-2009, 08:24 PM   #2
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How to check gas control valve?


Demand a raise if you are doing HVAC for the chumps.

How many wires connect to the vavle. If only two you should have 24 V.

Also there is a secondary limit mounted somewhere on top. Could be cutting out too.

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Old 01-30-2009, 12:28 AM   #3
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How to check gas control valve?


Here's a tip. If it does turn out to be a regulator issue and when you do find out the model number of the Honeywell unit (it has to be on there somewhere), go to their website and look it up here under "product search",

http://customer.honeywell.ca/Honeywell/UI/Pages/Catalog/SystemCategory.aspx?Catalog=Homes&Category=Gas+Val ves+for+Residential_2201&ChannelID={1D530037-45C1-4BA3-A615-415672F1662B}

If it is no longer being made they will suggest an alternate like they did for me when I had to replace mine. Kudo's to Honeywell for a great website and for providing so much information including installation information. I wish Robertshaw would have such a great site but ah well...
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Old 01-30-2009, 06:01 PM   #4
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How to check gas control valve?


Quote:
How many wires connect to the vavle. If only two you should have 24 V.
See photos below. Maybe some of you can help tell me which part is which.
I checked for current with VOM. None without call for heat. One terminal showing 25v after I raised the stat. Hard to tell you the wire without knowing what to call what and I haven't found how to edit the photos with info on them.
Here's how I will identify and reference for the time being:
A. There is a junction box for the incoming power supply for fan, etc.
B. There is a (?) transformer.
C. Gas valve.
D. Vent valve.

On the gas valve, at the top left there is a small oval section with two black wire side by side. Looks like an in-and-out setup. At the bottom right, there is a blue (my mind has gone blank) plastic board with several wires.

Also coming in are the stat wires that are connected to the transformer. Not sure what should be hot when. None are with no call for heat. The big red one with the white stat wire on the transformer are hot (25v) with a call for heat but there is no current anywhere else.

Maybe I covered everything I have been able to identify so far.
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Old 01-30-2009, 07:01 PM   #5
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How to check gas control valve?


Where is the t'couple? On a call for heat you should measure 24v where the two black wires connect to the valve.
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Old 01-30-2009, 08:00 PM   #6
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How to check gas control valve?


Thermocouple is tied in to the bottom I think. He should be able to just install a standard V800 gas valve. I would be concerned about cracks in the heat exchanger.
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Old 01-30-2009, 08:37 PM   #7
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How to check gas control valve?


In the second from the top picture, the terminals on the blue insulator are marked TH on the top left, TR beside it but they look like they are two terminals on the same post, bottom left is TH, and bottom rt is TR. The two black wires from the connector plug above are connected one to TH, and one to TR. Are these the two black wires you are talking about? There is no current at either terminal with call for heat.
The tcouple is on the opposite side of this view. You can see a part of the wire coming from behind the bottom and going into the burner section. I should have shot a pic of that, but I got tunnel vision on the wiring.
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Old 01-30-2009, 08:45 PM   #8
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How to check gas control valve?


In the second from the top picture, the terminals on the blue insulator are marked TH on the top left, TR beside it but they look like they are two terminals on the same post, bottom left is TH, and bottom rt is TR. The two black wires from the connector plug above are connected one to TH, and one to TR. Are these the two black wires you are talking about? There is no current at either terminal with call for heat.
The tcouple is on the opposite side of this view. You can see a part of the wire coming from behind the bottom and going into the burner section. I should have shot a pic of that, but I got tunnel vision on the wiring.

Oops,
Left the room for a minute and forgot I had already submitted.
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Last edited by downunder; 01-30-2009 at 08:48 PM. Reason: duplicate
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Old 02-03-2009, 08:48 PM   #9
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How to check gas control valve?


"Clean and tight" my daddy used to say as a mechanic. Anything that needed a gasket, clamp, or connection. In recent years I have heard the philosophy of KISS- Keep It Simple Stupid!

Final solution- rusty connection on the call for heat circuit at the terminal from the transformer to the lead going in to the valve. A little emory cloth....

Our "walks on water" shop mechanic disassembled the supply plumbing, took the valve out and took it most of the way apart, put it all back together, lit the pilot and declared it healed! I asked if he wanted to actually turn it on (call from stat) and see if it worked. I did that and told him that only the pilot was on but no heat. He found something else to work on so I had to start this saga from scratch. It's a little hard to see up a dark hole with bifocals, behind a heater, no head room, and the glare of the sun in one's eyes. Remember, this is in a greenhouse. So I got a flashlight-in the bright sun- and discovered the rust. Tried to clean it with some WD40 and scraping it with a pocketknife blade. Finally took it off so I could get it on a bench. Unable to find any model info but did find a faded out decal on the side. I'm beginning to ramble. After a good cleaning, I connected the source current, kicked up the stat for a call, and played morse code with the valve by touching the ground to complete the circuit. Put it all back together, turned the stat up, VIOLA! Hit it four times over the next couple of hours and it's still working.

Clean and tight!
Dedicated to the best troubleshooter I have ever known.

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