No gas from Pilot on new 720-400

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Old 12-06-19, 04:42 AM
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No gas from Pilot on new 720-400

Hi, my daughter house has a Weil Mclain PCG-4 series 6 boiler system and I have been repairing it the last few days due to it having issues. Replaced out the recirculate pump, new fill valve & expansion valve and last night I was installing a new 24VAC transformer & Robertshaw 720-400 gas valve. The gas valve is being replaced because it wasn't flowing gas to the main burners, but the pilot worked just fine. The transformer was being replaced because I was getting a fluctuating voltage of only 21 - 22VAC to the valve, so I figured I would replace it as well. Well, The valve is in, the transformer is in, but no gas flow to the pilot and I am at a loss as to why. The rest of the houses appliances that are gas, (Water heater & stove) are working just fine.
 
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Old 12-06-19, 02:16 PM
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Ras,
With the limited info given you didn't mention if you changed the thermocouple. The t-couple is a copper tube that goes from the gas valve into the chamber and is what tells the gas valve it's OK to light the burners on a call for heat.

This may sound foolish but did you turn the lever to the ON position on the gas valve.

One last thought. When you changed the gas valve did you bleed the air from the gas line to the pilot.

Hope this helps a little.
 
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Old 12-06-19, 03:51 PM
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What’s incoming and manifold gas pressure?
Gas valves require field setup so if you changed the valve hopefully you were aware they need field adjustment to the proper pressure.
 
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Old 12-07-19, 02:47 PM
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You're positive you've got the valve in the correct orientation? Inlet and outlet on the correct sides?
 
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Old 12-08-19, 07:07 AM
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Good morning, sorry for not answering sooner but the system here didnt indicate that anyone had responded to my post.

As for you question, yes thats the first thing I changed. Thermocouples are a quick cheap check.

Yes, I initially turned the gas valve to the on position to leak test the system. Once I ensured that I didnt have leaks, I then moved the lever on the gas valve body from off to the pilot position, grabbed the lighter, lit it and placed it by the pilot tube & thermocouple and depressed the lever to the set position and waited till the unit lit. It never did. Did this multiple times.
 
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Old 12-08-19, 07:11 AM
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Good morning, Yes I have the valve oriented correctly. The replacement valve is an almost identical replacement to the one that was originally there, and the arrow on the body indicating gas flow I have pointing in the correct direction. I do appreciate the response and assistance.
 
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Old 12-08-19, 07:20 AM
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I believe thats where my issue is. In my area, Consumers Energy provides the gas service at 7" WC to each residence, while the new valve is set to 3.5"WC.

I know that on the bottom of the valve there is an adjustment screw for the pressure regulator, which is probably where this needs to occur, but I do not have the information on hand to adjust it, and the locale HVAC company is 3-weeks out for service calls, so thats why I am trying to assist my daughter with all this.

What’s incoming and manifold gas pressure?
Gas valves require field setup so if you changed the valve hopefully you were aware they need field adjustment to the proper pressure.
 
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Old 12-08-19, 07:23 AM
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Are you sure the pilot orifice is clean? How long have you held the valve in the "set" position while trying to light the pilot? It's possible there is still air which needs to be purged.
 
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Old 12-08-19, 07:36 AM
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Hi, had the same problem it takes awhile to bleed the air from system, especially through the pilot line.
Geo
 
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Old 12-08-19, 07:38 AM
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Good morning,

I checked the orifice, dismantled the tube from it, blew it out with air and reassembled. Son-in-law is with Local Fire department, brought over their leak detector just in case something was amiss and we let it sit there for awhile while we took turns depressing the set lever and nothing. I believe that roughneck77 is probably correct with that it needs the field setup, but I don't enough information to adjust the pressure regular.
 
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Old 12-08-19, 07:42 AM
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Robertshaw 720-400 Gas Valve

Here is the gas valve that I installed. It comes preset to 3.5"W.C. from factory.
 
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Old 12-08-19, 09:05 AM
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Valves are not plug and play devices, they don’t come preset to work everywhere everytime. Different areas have different input pressure which will mean a different output pressure.
You’ll need a manometer for proper setup.
 
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Old 12-08-19, 11:34 AM
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Ras,
I mentioned the bleeding of air because once you opened up that gas line to replace your valve you now have that whole 1/2" gas line from the shutoff to the burner loaded with air that must be bled before your pilot will light and trying to remove it through the tiny hole in the pilot tube can be very time consuming. You must hold down the pilot button until you smell gas.

As far as you having to adjust the pressure most units only take 3.5" of gas pressure. Your boiler should have a plate with the info. The gas co. gives you 7" so you can supply all your appliances. 3.5" should be sufficient to run your boiler.
 
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Old 12-08-19, 03:23 PM
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I did bleed the lines as far as they would go. But, no gas would go beyond the valve body out into the tube to the Pilot.
 
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Old 12-08-19, 03:28 PM
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Valves are not plug and play devices, they don’t come preset to work everywhere everytime. Different areas have different input pressure which will mean a different output pressure.
You’ll need a manometer for proper setup.
You are correct, I figure that is my issue.

My other issue is that the local HVAC is three weeks out for the next available appointment and we have to wait till they can get to us. That's why I am attempting to get some assistance in the mean time.
 
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Old 12-10-19, 11:11 AM
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Well, I want to give an update. I installed a replacement valve that I received from that company and it too wasn't function as would be expected. So, I contacted a local HVAC company that had an opening monday late afternoon 12/9 and made arrangements for a service tech to come out. The tech spent the better part of an hour dumbfounded as to why the valve wasnt functioning as expected. He checked pressures, he checked voltages, he checked magnet strength, he ran the gambit on it and as he put it, "I'm dumbfound it." There was no reason the valve should be acting the way it was, so he concluded that I had received a second "defective" valve from the online parts house. He then proceeded to contact his boss and I was able to purchase one from him, I installed it and the pilot lit on the first try. No issues, no fuss, no nothing. I contacted the parts house this morning and explained what occurred and they immediately processed a RMA for the part and said I will get my CC credit back as soon as they receive it. Strange, how can you get two valves from the same manufacturer, same type, same everything, both defective. The tech guessed that maybe they had been sitting on the shelf for some time, other than that, we haven't a clue as to why they both failed.

Thanks for all the help guys.
 
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Old 12-10-19, 02:10 PM
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Sorry to hear about your bad luck with new parts, but glad you got it up & running. Thanks for the update.
 
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Old 12-10-19, 05:57 PM
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It wouldn't be unheard of for a distributor to get a bad batch of parts.
I'm sure they'll look into the problem at their end too.
 
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Old 12-12-19, 10:27 AM
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Is there a way to mark this thread as being solved?
 
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