Main burner issue

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Old 10-18-08, 07:41 AM
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Main burner issue

Hello, I have a NG Heil about 25 years old. trouble is the main burners wont light. originally the on off switch which is a push down and turn button broke and would not lock into the on position. When I would hold down button in place by hand pilot and burners lit and ran fine. I replaced the button and now button works properly, pilot ignites and remains lit but burners dont fire. so pilot just burns. I do have spark from flame sensor at main board so the flame sensor seems to be working fine. I have 3 wires PV, MV/PV, and ground running to main board. it is an intermitten spark set-up so for some reason the signal isnt telling the burner gas valves to open so pilot can ignite.. any advice is deeply appreciated. thanks.
 
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Old 10-18-08, 08:15 AM
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Main Burner issue flup:

The igniter unit has what appears to be a high tension lead going from the end of it to a box made by Honeywell. There is also a grey ground wire coming from the unit's mounting bracket that goes to the "ground" terminal on the same box.The exact model of the furnace is NUGK050LF02. I found a picture of the igniter assy online. It can be viewed here:

http://www.expertappliance.com/heil-heating.html

It is about 1/3 of the way down the page and is called a "Pilot Igniter Sensor"
The only way I can figure is that the Honeywell box sends out a high voltage to the unit in order to fire the spark, and then waits for a signal coming back on the same line telling the microprocessor that the flame is present and it is okay to fire the secondary part of the gas valve and thats not happening.. The valve has three wires going to it and I figure that it must be a two stage valve.
Am I correct so far or am I going down the wrong path? Do any of you guys have any experience with this type of assembly?
 
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Old 10-18-08, 09:14 AM
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Can you see well enough, that assembly you had a picture of, to determine if it sparks? If you can't see it well, you should also HEAR the spark. The spark jumps the electrode, but then also, the electrode, I believe with this particular unit, serves as a sensor.

You need to test at the Honeywell box if you have 24 volts coming into the power or thermostat connection on it. You can test with a meter between it and ground, to see if it has 24 volts when the furnace is calling for heat.
If yes, then we know the power feed to the Honeywell box is good.

After a number of seconds delay, you should get the spark. If you are not getting any spark out there by the electrode next to the pilot flame hood, then you have to figure out if the reason is something wrong in the Honeywell box (you'd have to replace it if there were) and the entire wire and spark/sensor assembly. The wire needs to be good. The grounding of the sensor needs to be good. (If you end up having to remove this entire assembly, make sure connections are good, nothing broken and not badly corroded.) The electrode needs to be clean and gapped right. If all this were good, you should have spark. If not, each of these has to be investigated.

You can quickly determine if it is the Honeywell box at fault(if you have confirmed 24 volts is going into it!), or one of the other things I said, by removing the spark wire from the Honeywell box and rig up some other wire, screwdriver, or whatever that conducts electricity, and seeing if you can make a spark jump beween what you are using (do not touch any metal with your bare hands/fingers!) and the metal of the furnace. If you have 24 volts coming into the box, yet no spark with this test, and you are say holding the end of what you are using about 3/16ths inch away, then your Honeywell box is shot.

But if you do get sparking, then you have something wrong with either your spark wire, or the spark wire's insulation is bad and current is leaking through it and jumping to the furnace's sheetmetal instead, of something is wrong with the electrodes with being badly worn or broken or very tarnished up or something. And you would have to remove this assembly and inspect, as I earlier said.

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

Oddly enough, early this morning I was reading my ladder schematic on a Johnson Controls module I recently installed in a big air handling unit, and noted that many furnace's modules can be ladder tested in similar fashion.
 
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Old 10-18-08, 09:57 AM
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The pilot remains lit and there is spark between the honeywell and the red spark wire. I held the red wire just over the spark plug type connection on the HW box and there is spark.

The only spark I get (rapid clicking sound) is when the furnace starts up after I have used the t-stat to call for heat. This initial spark ignites the pilot which does lite and remains lit, after that nothing...........no secondary spark. Does the pilot lite the main burners or should there be a secondary spark?

If I remove the red PV wire at gas valve pilot dies and clicking begins and there is visible current spark....... reconnect and pilot lites.

If I remove the tan PV/MV wire at gas valve pilot dies and clicking begins also there is visible current spark........reconnect and pilot lites.

If I remove black MV wire at gas valve pilot remains lit but there seems to be no visible spark of current.......thoughts??????
 
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Old 10-18-08, 10:03 AM
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Is there a way of jumping the MV terminal at the gas valve to test burners using either the PV or MV/PV wires which do have spark?

I hope to make sure gas valve itself is at least working properly.
 
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Old 10-18-08, 10:47 AM
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No sense trying to jump the gun. The sparking is independent of the gas, and we need to know if you are first getting spark down there at the electrodes inside. The PV current will not exist until you are at least getting that current for sparking. And there may be a slight delay even in that signal.

Rarely is the probelm the valve, in my experience, anyway. And that deals with new furnaces and the old dinosauers from the past.
 
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Old 10-18-08, 11:56 AM
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Originally Posted by atleasttry View Post
The pilot remains lit and there is spark between the honeywell and the red spark wire. I held the red wire just over the spark plug type connection on the HW box and there is spark.

The only spark I get (rapid clicking sound) is when the furnace starts up after I have used the t-stat to call for heat. This initial spark ignites the pilot which does lite and remains lit, after that nothing...........no secondary spark. Does the pilot lite the main burners or should there be a secondary spark?

If I remove the red PV wire at gas valve pilot dies and clicking begins and there is visible current spark....... reconnect and pilot lites.



If I remove the tan PV/MV wire at gas valve pilot dies and clicking begins also there is visible current spark........reconnect and pilot lites.

If I remove black MV wire at gas valve pilot remains lit but there seems to be no visible spark of current.......thoughts??????
Per your PM. Sorry, I did not see this post. I will get back to you here, regarding what you did.

The pilot only is what lights the main burners. If that is not happening though, then you have to see if you have a click sound and 24 volts going to the MV terminals a few seconds after the pilot lights. If not, then you either have a bad sense for pilot flame or a bad Honeywell.

But if you measure for 24 volts at the MV terminals on the gas valve when the pilot first lights, and there is no 24 volts at the MV terminals at gas valve, but then a number seconds later there IS - then the gas valve MAY be bad. But it could also be gas line/orifice obstruction right near the pilot, and you would have to test for that. How? I am almost afraid to say to a novice, as to how to go about checking to see if gas is coming out of the valve or not, if the MV is activating. The key words are 'IF the MV current shows up after the pilot'.

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

I have to go on errands for a while.
 

Last edited by ecman51; 10-18-08 at 12:13 PM.
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Old 10-18-08, 04:20 PM
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Ok thank you I will check back later tonight for any more advice.
 
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Old 10-18-08, 08:27 PM
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Furnace help

Are you sure the system is not telling the valve to open. Have you checked to see if you have 24 volts between MV and MV/PV.
The only reason I ask is that you said you repaired the valve.
 
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Old 10-19-08, 07:26 PM
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I do have a multimeter, how exactly do I test? on the main board or at the gas valve?
 
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Old 10-19-08, 08:08 PM
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Gas Valve

Either but it will probably be easier at the gas valve. If you have a pilot flame and 24 volts read between MV and MV/PV. Your gas valve is bad if no voltage the flame sensor is bad or possibly a loose connection. Most times I take apart and refasten all the connections to resolve grounding issues.
 
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Old 10-19-08, 08:31 PM
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I read 24V at PV and 24V at MV however I read nothing at MV/PV.

If I remove MV/PV at the gas valve the pilot ceases, reconnect and I hear the gas valve open and pilot re-ignites.

How can this happen when I get no read at mv/pv on the board or the valve??? Thoughts???
 
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Old 10-19-08, 08:52 PM
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Gas Valve

MV/PV is the common that is why I said read between MV and MV/PV. But it sounds like you have a bad gas valve.
 
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Old 10-19-08, 09:35 PM
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I thought the Honeywell box sends out a high voltage to the flame sensor in order to fire the spark, and then waits for a signal coming back on the same line telling the microprocessor that the flame is present and it is okay to fire the secondary part of the gas valve and its that return signal thats not happening. If the gas valve was bad I shouldnt have pilot right??
But I do hear valve open to light pilot it just isnt sending gas to the burners. where do I check into why that second signal isnt happening??
 
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Old 10-19-08, 09:49 PM
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No. Although I have no hands-on experience with this particular furnace I can tell you that the ignition spark does NOT travel on the same wiring as the flame signal. If the pilot ignites then there is nothing wrong with the ignition module or the pilot valve. The flame sensor on the pilot will stop the spark AND advance the system to opening the main valve. There is no flame sensing on the main flame, the assumption is that a properly burning pilot will always light the main flame.

My feeling is that your "repair" to the knob on the combination gas valve is the problem although it is possible the operator on the main valve is not opening the valve.
 
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Old 10-19-08, 10:07 PM
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The repair was simply pop broke knob off and popped new knob on,

Please review my second post in this thread, there is a link to a picture of my flame sensor, it is spark and sensor in one.

Valve opens at spark and ignites pilot perfectly and 24V is present on MV immediately after pilot, just no gas for burners

are there two seperate valves in gas valve assy???
 
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Old 10-20-08, 10:50 AM
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yes there are to valves in the valve body when you have 24 volts to pv (pilot valve) the gas goes to the pilot when you get 24 volts to the mv (main valve) the gas goes to the burners mv/pv has no volts. i dont no if this will help you or not but i had a similar problem with a heil furnace i changed the gas valve (honeywell vr 844) and it still had the same problem someone told me it could be the pressure switch did you check the pressure switch to do this pull the 2 wires off of it and jump them together but be sure you pull them off first and do not use the furnace like this because it could mean the vent is pluged by something if this is the problem check that the vent is clear if it is change the pressure switck
 
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Old 10-20-08, 02:48 PM
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Gas Valve

If you have 24 volts to the MV and MV/PV terminals and there is no gas coming out either the gas flow is restricted or the gas valve is bad once again. There are 2 coils on your gas valve one is for pilot and one is for the main valve I did not want to say this but since it has already been stated your rebuild of the switch is probably at fault but because you did not have heat before that So What!! Just replace the gas valve and you will probably be OK.
 
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