Gas Valve Question

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  #1  
Old 10-19-08, 11:56 PM
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Gas Valve Question

On a Heil Model NGUK050LF02 Main burners do not light. Pilot lights fine and I read 24V at terminal MV at gas valve immediately after pilot ignites but there is no SECOND click opening main burner valves. any ideas???
 
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Old 10-21-08, 09:21 AM
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You said you had 24 volts at MV after pilot lit, but did you only have it after the pilot lit, or before as well?

If I come across one of these 3 wire valves I wil see what it does, and get back with you. I know we have some of these systems out there in the rentals, but the addresses I can't remember. I got to think - at what place may have pilot lights.

I know that sometimes testing 24 volts can be a fooler, dealing with it's potential. I had a 10-connection 24 volt relay for a boiler, where no 24 volts could be found on any terminal, whether between any two teminals, nor from any one terminal to ground, and yet the relay clicked and worked, as an example. But current could be found at the wires (when disconnected).
 
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Old 10-21-08, 02:45 PM
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Actually the 24V reading on MV comes immediately AFTER pilot lights there is no reading prior to pilot ignition and it is a steady read.
 
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Old 10-21-08, 03:27 PM
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Originally Posted by atleasttry View Post
Actually the 24V reading on MV comes immediately AFTER pilot lights there is no reading prior to pilot ignition and it is a steady read.
Well mv is the main valve operator.. Seems like a bad valve.
 
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Old 10-21-08, 03:58 PM
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The one I had an opportunity to test today, on a Heil furnace, gave me voltmeter reads as follows: Upon call for heat, as soon as pilot to light, I got digital voltmeter number fluttering between PV and PV/MV (or from PV to sheetmetal.). When the burner fired up almost immdiately after the pilot came on, I got the 24 volt MV reading ONLY if I had the black meter lead on MV and the red lead on PV/MV (or from MV to sheetmetal). And it stayed at 24 volts.

So based on this and what Mbk3 thinks also, it doesn't look promising. It really does seem that if you really do not smell or feel any gas coming out of the gas valve, and you are certain of this (as we had discussed) -then it must be the valve.

I can't recall whether you said that this is the first fire up of the season or not. Also, did you say that you did get it to fire up once, but then couldn't any more? Was that you? Would like to know that, to rule out that some sort of adjustment had been made to anything with the gas valve. Also, is this natural gas?

Since coincidently today I too checked out a Heil, maybe these are the same gas valves. Please describe the valve and/or post numbers that are on it, and when I go back to the rental tomorrow to work on their storms, I will check it out and see if I can see anything else interesting about that particular valve, if we happen to have the same one. Also, I can call up my local supplier and find out what a new one costs, here, and we can compare.

......................................................

After reading McNealyln's new thread about same problem, with almost the same furnace, I got thinking that if that Heil of yours has a flame sensor for the burners ( I forgot to look on the one I checked out today for you, but will tomorrow), that means when you did your gas valve smell or feel test, and you said no gas came out, when the MV was energized, that if there is a flame sensor, that gas valve would shut down in only a few seconds. So unless you were prepared to smell and/or feel, and catch that in that 3-4 second window, then maybe you did not notice if the gas really came out or not! You have to be certain no gas comes out so you too do not waste your money on a new valve, the way Mcnealyln just did! Keep in mind that often the gas smell is not that great and the pressure is low(with natural gas), also.

If you have natural gas, you will have a gas meter with a 1/2 foot dial on it. You might run the furnace (or have someone turn it on to call for heat when you get out by the gas meter), to see if when the pilot comes on and makes the dial spin, that immediately right after that you do not see the dial spin faster for 3-4 seconds and then slow again to just the pilot gas consumption speed. If the dial does speed up for those 3-4 seconds, then gas IS coming out the main gas tube.
 

Last edited by ecman51; 10-21-08 at 04:35 PM.
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Old 10-21-08, 07:00 PM
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Originally Posted by ecman51` View Post
The one I had an opportunity to test today, on a Heil furnace, gave me voltmeter reads as follows: Upon call for heat, as soon as pilot to light, I got digital voltmeter number fluttering between PV and PV/MV (or from PV to sheetmetal.). When the burner fired up almost immdiately after the pilot came on, I got the 24 volt MV reading ONLY if I had the black meter lead on MV and the red lead on PV/MV (or from MV to sheetmetal). And it stayed at 24 volts.

So based on this and what Mbk3 thinks also, it doesn't look promising. It really does seem that if you really do not smell or feel any gas coming out of the gas valve, and you are certain of this (as we had discussed) -then it must be the valve.

I can't recall whether you said that this is the first fire up of the season or not. Also, did you say that you did get it to fire up once, but then couldn't any more? Was that you? Would like to know that, to rule out that some sort of adjustment had been made to anything with the gas valve. Also, is this natural gas?

Since coincidently today I too checked out a Heil, maybe these are the same gas valves. Please describe the valve and/or post numbers that are on it, and when I go back to the rental tomorrow to work on their storms, I will check it out and see if I can see anything else interesting about that particular valve, if we happen to have the same one. Also, I can call up my local supplier and find out what a new one costs, here, and we can compare.

......................................................

After reading McNealyln's new thread about same problem, with almost the same furnace, I got thinking that if that Heil of yours has a flame sensor for the burners ( I forgot to look on the one I checked out today for you, but will tomorrow), that means when you did your gas valve smell or feel test, and you said no gas came out, when the MV was energized, that if there is a flame sensor, that gas valve would shut down in only a few seconds. So unless you were prepared to smell and/or feel, and catch that in that 3-4 second window, then maybe you did not notice if the gas really came out or not! You have to be certain no gas comes out so you too do not waste your money on a new valve, the way Mcnealyln just did! Keep in mind that often the gas smell is not that great and the pressure is low(with natural gas), also.

If you have natural gas, you will have a gas meter with a 1/2 foot dial on it. You might run the furnace (or have someone turn it on to call for heat when you get out by the gas meter), to see if when the pilot comes on and makes the dial spin, that immediately right after that you do not see the dial spin faster for 3-4 seconds and then slow again to just the pilot gas consumption speed. If the dial does speed up for those 3-4 seconds, then gas IS coming out the main gas tube.
A constant 24 volts at mv to mv/pv or ground indicates pilot has been proven by flame signal/sense. Valve operator is failing to open.
 
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Old 10-22-08, 07:07 AM
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Originally Posted by mbk3 View Post
A constant 24 volts at mv to mv/pv or ground indicates pilot has been proven by flame signal/sense. Valve operator is failing to open.
Just so everyone reading this is clear: Do you mean that if you test 24 volts from MV to MV/PV, that the main gas valve should be open in that condition?
 
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Old 10-22-08, 09:48 AM
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Originally Posted by ecman51` View Post
Just so everyone reading this is clear: Do you mean that if you test 24 volts from MV to MV/PV, that the main gas valve should be open in that condition?
Yes. Voltage is being applied to gas valve and it should open. He has stated the pilot valve has opened and the pilot is on. Further he states there is 24 volts to mv and that is the end of the line. Kinda like a light bulb....if you have voltage at the socket the light should come on unless the bulb is no good. Sound right?
Of course there could be other circumstances..such as a spider nest(s) blocking the flow, very very doubtful.
 
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Old 10-22-08, 03:33 PM
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Thanks Mbk3.

I knew the answer. Just had to be certain that is what you meant, and that everyone else did.
 
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Old 10-22-08, 04:04 PM
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Atleasttry,

Pretty odd how you get it to fire sometimes, and not other times.

Have you made any more checks to be certain gas is not coming out -perhaps coming out some, but not quite the required amount? On the Heil I was at today #NUCK075AG02, mine has the burners and orifices right out there in the open, right near the front. If you also have that, maybe you should try to take a mirror and inspect them orifices first. Then try to ream a pin around through the hole. And then soap test the orifices.


It is too easy in this business, along with many other trades, to make a misdiagnosis due to taking things for granted. For instance: Yesterday, we had a poster who did not check his filter. Today, I almost wasted $100-150 (one supply house wanted $100, the other supply house wanted $150 ) for an ignition module for a York Luxaire. I DID put in a relatively inexpensive HSI ($20), as I had 120 volt current to it AT THAT TIME (the fooler!), and it ohmed kinda high at 165. So I install it, fire up the furnace and it ran fine for 3 cycles -then quit! I ended up opening the furnace, undoing what I had done, retested and found THIS TIME that no 120 volts now to HSI! So I suspected the module. Turns out, care and dillegence won out, and I found that by spreading the split pins in the jack connector at the module, that this made for a better connection(not an obvious problem since the plastic jack felt like it plugged on tight!) and solved the problem. Anyway. Whew! Close one - the way I'd have current one minute and not the next.
 
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