Seattle Pioneer Help Clarify previous post on Pilot wont light

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Old 01-14-13, 01:47 PM
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Seattle Pioneer Help Clarify previous post on Pilot wont light

hello new on here and was reading a previous old post about a pilot not lighting on a gas furnace... I have the same setup a Robertshaw 780-715 and 7100 DER-57C gas valve and the pilot wont light but when I turn the gas valve on the 7100 on and off rapidly it will light... You gave this answer on a similar problem>>

"Also make sure that the gas hasn't been shut off at the electric gas valve, which probably has an "on" position, and that the furnace shutoff valve is on.


If that's the case, the pilot light may be plugged up, preventing gas from flowing. Loosen the brass ferrule compression fitting that holds the pilot tubing in the gas valve and see if you have gas coming out when you have the furnace switched on as you describe."

So I have checked voltages, I have good spark, all gas valves are on including meter.. and when I turn the gas valve (7100) on and off rapidly (I hear slight poofing) it will light but takes a lot of times 10+ And, the furnace will run normally untill its not calling for heat and turns off not to restart! SO i'm thinking maybe the pilot line is somewhat plugged as you suggest... But to clarify your second paragraph,>> "Loosen the brass ferrule compression fitting that holds the pilot tubing in the gas valve and see if you have gas coming out when you have the furnace switched on as you describe" Are you meaning the brass ferrule where its screwed into the gas valve while the pilot starter is sparking?? Im a Electrician and Instrument tech but not sure Im understanding you or not.. Im Not sure if its real low pressure, or how much gas would come out... Or do you mean to turn off the gas to the gas valve and unscrew it and blow out or?? I had this problem about 5 years ago and kept messinng with it and its run great until this year. Is there an adjustment for the gas going to the pilot on the gas valve that could be set maybe to low?

Anyway SP thanks for helping everyone.. I know it takes a lot of time... I just want to do everything the safest way possible... Thats engrained in me after 40 yrs in the electrical trade

Thanks again,
Asparky
 
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Old 01-14-13, 07:11 PM
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When the thermostat is calling for heat, 24 VAC should be switched on to the TH terminal on the ignition control. When the thermostat is not calling for heat, the votage should be near zero.

Check to see if that's happening.

If so, when the thermostat is calling for heat, 24 VAC should be switched on to the PV terminal, you should get pilot gas flowing to the pilot light and the spark should turn on. check to see if that's all happening.

Based on your description, the pilot gas isn't turning on as it should. If the 24 VAC isn't present as described, that could be the problem.

If the 24 VAC is present and there is no pilot gas, you might have a sticking gas valve or you might have a pilot burner that's plugged up.

Take a wrench and loosen the brass fitting that holds the pilot tubing into the gas valve. When the power is turned on, you should get an obvious flow of gas coming out that fitting on the gas valve. If you do, you probably have a plugged up pilot burner and pilot orifice.

If you don't get gas flowing out the pilot fitting on the gas valve, you probably have a bad gas valve that isn't opening properly.


*** Caution! *** You wont have a huge amount of gas coming out that gas valve pilot fitting, but you should probably shut off the gas valve at the manual shutoff valve at the furnace, and turn the valve on briefly to see if gas is coming from the gas valve as described.




Report back on what you find.
 
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Old 01-14-13, 10:17 PM
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Thanks SP

The house is vacent and about 15 miles away. I figured there wouldn't be much gas there (at gas valve pilot outlet) just didnt know for sure.. So heres what I did I checked for 24VAC across the C and P terminals of the gas valve and it was there

So figured the MV/PV and PV OK with no faulty wireing between control module and gas valve (sorry about the large font Im having computer issues also )

I then turned the gas off at the main by the furnace and disconnected the pilot line at the gas valve and blew it out good with compressed air and some into the hole of the gas valve...

I briefly turned on the gas and didn't smell any so hooked it up and also adjusted the pilot adjustment screw just a touch, and tried it again... Pilot lit nice but it kept sparking for several minutes with a nice pilot flame but gas valve didnt let main gas flow and furnace didnt start... after a few minutes I reached in and shook the pilot assembly it quit sparking and the furnace started..

I seem to remember about 5 years ago this doing the same thing. I think the 2 wires going to the pilot assembly are problematic and I may have had a plugged up pilot tube... Im not sure if it will be working tomorrow but will see. I did this early this afternoon and will go again tomorrow and check things out...

3 things I'm not sure of are 1. the size/length of the normal pilot flame and 2. does the pilot remain lit while the furnace main burner is operating. and 3. is there an orfice in the gas valve pilot outlet and what usually plugs it up? bits of rust?


Will post back after I go back over

thanks for the help

Asparky
 

Last edited by lawrosa; 01-15-13 at 01:10 PM. Reason: edit for clarity
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Old 01-15-13, 01:00 PM
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If you want to do your own troubleshooting, help yourself.

But if you don't answer the questions posed, I can't help you.

Frankly, I can't follow your last post to understand what you've done. And shaking parts and such is not a diagnostic procedure.

Sorry I can't help you.
 
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Old 01-18-13, 05:59 PM
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Hi SP
Sorry, I did the troubleshooting on my own before I got back home and heard from you...Below freezing here and had to try and get her going. when I checked, Everything was normal as it should be. after I blew out the pilot tubeing and adjusted the pilot flame it has been running fine and didn't want to mess with it until it warms up a little. I messed with the wiring because thats what electricians do and I had remembered it had been problematic a few years back. I wasn't discounting anything you suggested, matter of fact I blew out the tubing as I think you suggested on this and a similar post (the reason for my first post to clarify) So you did help me and I appreciate it. when I don't have to worry about the pipes freezing up in the house I'll probably troubleshoot/ rebuild the pilot assembly as it has been problematic in the past. Thanks again for all your help!
Regards,
Asparky
 
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