Gas "wood" stove shuts off

[coaly]

The control with hi and lo only controls how much gas flow goes to the main burner when that portion of the valve is ON allowing gas flow to main burner. It is how much heat is produced by the main burner and how much heat will go into the building.

The orifice size measurement is more critical than a picture would show. It may be stamped with a number or you would measure with a drill bit until you know the exact size in thousandths of an inch. If it was a propane orifice you would have very small flame to none at main burner. The orifice size is twice as large from LP to Nat. Your burner should be BLUE down at the bottom of flame at burner and only have yellow tips. If so, it is the correct orifice.

Back to your problem;

You should be able to troubleshoot what is wrong with just your eyes.

The PILOT should be all blue. Which is critical for keeping the thermocouple generating the proper current to keep gas valve open. With pilot only on, it is doing that as it should.

Look at the flame as it cuts across the thermocouple with pilot only lit. This is the correct flame generating the correct amount of voltage to keep the gas valve open as it should.

Now turn on the main burner and watch the pilot flame. It should stay the same, not waver, not move away from the thermocouple.

IF it does, you probably have an air leak from around the glass or some other leak into the burner "chamber" rushing into the combustion chamber area. This will allow the thermocouple to cool down and shut the gas flow off through valve. Lets verify if that is what is happening first. Simply watch the pilot flame to see how long it remains lit before shutting down.

 

[stevengrahek]

OK. It is definitely a NG orifice. The burner flames are blue based with yellow tips.

The pilots are blue flame, but they do flicker a fraction of a second, about every second. Could this be the cause? The pile and couple both seemed to be engulfed in flame. I will try to take a video tomorrow and post it.

about that hi lo dial. yes, that what I thought it was for. however, when dial is attached with the center screw the dial swings without catching anything. if the dial is removed, and then the plunger unit that screws into that inlet is removed, the flame goes to low, but if the plunger unit is screwed back into the inlet, it goes to high. and there is no way to get it down using the valve.
anyway, not that important if it is OK to have it on high all the time?

spg

 

[coaly]

Yes, it can remain on high........

The portion of the valve that works the safety is the black plastic knob. When in pilot position it pushes inward which moves a steel rod inward with a spring pushing it back out when you let go. When the thermocouple is generating electric current, the electromagnet inside the valve holds the steel rod "IN" so gas can flow through valve. You're generating enough current to hold the valve open as well as generating enough current to open the main gas valve with power from thermopile. So the pilot flame is hot enough to generate enough power.

The glass must be in place to light this appliance, not leak around the edge, and make sure where the pilot line comes through the box into burner chamber there is no indoor air leaking into burner chamber. That will cause the pilot flame to move around when main burner is lit and not be in the correct position heating the thermocouple correctly when main burner is on.

I'll explain in my next post how a direct vent appliance gets oxygen into the sealed burner chamber for oxygen to get to the pilot and main burner. Then you will know what to look for.

 

[stevengrahek]

Hello again. Am afraid I am too much the amateur, in that, I have been testing the system with the fire box removed from the cast iron casing, and not always with the vent pipe re-attached. Doing that will invalidate the results, right? because air comes down and messes with the Pilot?

This stove is designed without access from the front when it is in its cast iron casing. So I have to remove the box, then remove the glass plate on the front to access the pilot, burner etc.

I did go on line and found a Vermont Castings generic manual, and it seems to be accurate for the configuration of the valves, pilot carriage etc. for my stove.

file:///F:/Drive%201/aaSteven's%20%20documents/6900%20GRASSWOOD/2016%20ART%20STUDIO%20REMODEL/Gas%20fired%20woodstove/vermont%20casting%20manual%20very%20similar%20to%20ours.pdf

but of course the valve has updated hi lo type switch, as far as that dial is concerned. and I believe the gas valve terminal block is updated but just vis a vis the type of connectors used, not the actual terminal labeling.

spg

 

[coaly]

The difference between direct vent and using indoor air with a chimney pipe opens an entire complex scenario with other factors to consider.

A gas burner is normally in contact with the atmosphere such as a range top burner or BBQ grille burner outside. When you put a burner inside a sealed burner chamber, it no longer has free atmospheric air pressure to push into it. I'll explain;

Any gas burner has a mixing tube portion of the burner. After the gas comes through an orifice, raw fuel mixes with oxygen in the mixing tube portion of the burner, before coming out the small holes where it is ignited. Gas comes through orifice at the correct pressure provided by a pressure regulator. AIR enters due to gas pushing the air (atmosphere) out of the burner tube. Atmospheric air pressure PUSHES air into burner to mix with fuel. This intake of air is at the air intake adjustment of burner. This is the basic flow that must happen to have proper combustion from any naturally aspirated gas burner. (aspirated from atmospheric air pressure, not a combustion blower which you don't have) Even a small pilot burner has a mixing tube with an air intake hole because raw fuel won't burn until mixed with oxygen. (roughly 70:1 ratio)

When you have a burner inside a chamber sealed from indoor air, you no longer have atmospheric air pressure to push air into the burner to mix with fuel. The venting system (exhaust out, air in) must be engineered to work properly.

Hot exhaust gasses rise, so it is critical to have enough vertical rise in the exhaust configuration to create movement upward and out of the burner chamber. This upward movement is measured in draft which creates a low pressure area in burner chamber which allows the higher atmospheric air pressure to enter (push) into intake, bringing fresh oxygen into the burner chamber. This is where the oxygen for mixing with fuel comes from.

If venting is not correct, you no longer have atmospheric air pressure at air intake of burner. The gas coming in can't get enough oxygen to mix with the fuel causing a rich air / fuel mixture which is where the black soot comes from. Too much fuel, not enough oxygen. In your case, this is configured by the manufacturer and would be specified in the installation manual as how much rise is required and how much horizontal run would still allow the correct amount of draft to create the proper intake air pressure. We don't know the exhaust / intake configuration to tell you if you have the correct amount of oxygen getting to your burner. So you can only go by how much yellow flame you have. Blue is hotter and burning clean, yellow is carbon or a carbonizing flame which deposits carbon in the form of soot on any cool surfaces it comes in contact with. This can be the glass, logs, or vent. As you know it makes a mess. The blue flame should be enough to clean the unburned fuel in the yellow flame to prevent carbon accumulation.

Now, on to your problem; When the main burner is on, we have a low pressure area being created by the draft exiting the chamber. This will allow the higher atmospheric pressure in the home to PUSH into any opening it can which will be the cause of the pilot to waver and not heat the thermocouple correctly. It's like getting a blast of air causing the flame to no longer be correct to heat the thermocouple correctly. That is what I'm suspecting is happening. It is the most likely cause and common when there is an air leak into burner chamber.

 

[coaly]

You posted your last post as I was composing that book, so Yes....... it has to be installed in the sealed burner chamber.
(someone help DAKSY off the floor )

It becomes more complicated being direct vented, but you should understand the principals to install and work on it.

Going back to venting to get the proper air into the sealed chamber;
Your picture shows a minimum amount of rise that may or may not create the draft required for the proper flow out and back in.
It would have been better raised higher to create more draft. That may be the cause of sooting due to lack of oxygen. I didn't look at the VC manual, but vent configuration requirements would probably be close to that manual.

Was soot on the vent or outside as well? That's a sign of improper venting. Units comparable to yours that I've installed have needed to be higher.

 

[DAKSY]

I'd say it's the correct orifice. That's not the cause of your sooting.
Generally it's the air shutter on the origin of the burner.
It regulates the combustion air mixing with the fuel to optimize the Air-to-Fuel ratio for the presentation of the flame.
LP and NG burn blue. As you close the shutter & reduce the ATF, the flames get yellower (LEANER)
If the shutter is closed too much, not enough O2 mixes with the incoming gas...It runs RICH...
It can also be caused by mis-positioned logs, lava or glowing embers.
They also mess with the combustion, but in a smaller way
The third cause can be in the venting, if it's incorrect or is malfunctioning...
Exhaust gases can be drawn into the combustion side & the spent oxygen screws with the ATF,
again by causing a RICH condition...

 

[stevengrahek]

OK. thank you for hanging in there for me DAKSY AND coaly.
I returned the firebox to the cast iron casing; making sure it was air tight as possible. hooked up the direct vent, which is a one foot vertical riser from top of unit, 90 elbow, one foot to wall receiver. according to the Vermont Casting manual I am subbing for lack of one, that is acceptable, ie above black cut off line, but in a gray zone. and yes DAKSY, those pipes have a lot of fine black soot inside them (so maybe I need another foot or so of rise (more horizontal pipe would be problematic for this installation, but vertical can be accommodated)?

The stove pilot lights and burns as in attached video. Lights up the main burner, which settles down into a yellow tipped blue flames. Everything is wonderful, for about 20-30 minutes, and bam, all gas gets shut off.

So? Are the millivolt readings being low still a possible problem. Should I try the readings after about ten minutes of the main burner being on?

Is the soot in the stove pipe an absolute indicator of need to increase vertical pipe? (I have added more air at the orifice area, and the flame seems to bluer than previously. So maybe less soot being made, and only the thermocouple/pile is the problem?).

have order new webbing to be sure glass front seals completely, but are those small yellow tips really an indicator of air seeping in?

thanks for any help you might suggest.

steven

 

[DAKSY]

Watch the flames. Do they seem to be "lifting" off the burner (aka ghosting)?
If so, that may be an indicator of your problem.
A blockage in the intake side (outermost diameter) of the venting.
Make sure it's clear & the exhaust side (innermost diameter) is securely attached...

 

[coaly]

I don't believe 1 foot rise is near enough to make enough draft to get air into the burner chamber. (same as a blockage not allowing air in) I would personally make it about 3 feet rise with 1 foot horizontal if possible...... Lack of air not only creates soot, but affects the pilot with lack of oxygen. When it's burning on high, take note of the pilot flame. Does it look exactly like it does when pilot only is on? It may "lift off" the pilot burner or even go out. If this happens, current from the thermocouple ceases and the safety valve closes.
Black soot and going out, I'd guess it to be starving for air since the pilot looks good and thermocouple generates enough when only pilot was lit.

The thermopile in your unit creates electric current to open main burner valve. So if that is weak, the main burner will go out or not light.

The thermocouple creates the electric current to hold the safety valve open, which is what is closing when the entire unit shuts down. We know it is generating enough current when only the pilot is lit since the electromagnet held the safety open for 2 days. Something is allowing the thermocouple to cool enough to not produce enough current to hold the safety open. You should be able to see it, such as the flame tip bending and not cutting across the thermocouple tip. Also the pilot flame may get yellow tips with main burner on.......The pilot looks plenty strong in video.

You could also try timing it on low or medium flame. When this appliance was working, was the burner control set to high? The higher setting will consume more oxygen and possibly not make much more draft (lower pressure area in burner chamber) to compensate for more needed air.