Bill Kielb

I agree with you, bisque firing - cone 04 just to sinter the material. Don’t want to make it really hard to glaze, assuming she wants to glaze it. All of my porcelains are bisqued to 04.

Since it is difficult to keep the iron particles in suspension, maybe it would be better to spray the glaze without the iron and then sprinkle the iron particles with a salt shaker onto your pot while the glaze is still wet...

@Bill Kielb @neilestrick
Thank you so much!!  
Bill I’m so impressed and grateful for the time and energy you took to help me out! I have been trying to fix this since last year when I received the kiln but nobody had a clue …and in just one day you fixed it!!!  It took a long time and effort for me to get a kiln and I was devastated  because I couldn’t use it.  I can’t express how happy and relieved I feel!! God bless you!! After all this time,  I am about to finish my first glaze firing with the temporary set up, the kiln is cooling now and everything is going great! 

I will follow the advice and update with pictures and results so more people like me can find this post in the future and fix similar issues easily. 
This is a great community and you guys are amazing, thank you so much! 

@Aurea The good news is we likely don’t need to do massive calcs and I can make some assumptions from your ambient air temps. The also good news is your 40 amp SSR likely easily operates at 60 c or more which is usually minimum design terminal temps. The somewhat hard part probably is pick a right sized computer fan that is 240v and maybe for simplicity it operates whenever plugged in. That kiln has no low voltage or neutral so 240v computer fan is likely easiest. Will chug some number later and add here to confirm reasonable size fan in CFM. Not likely to be gigantic.  (Break time at work - pretty busy morning) meanwhile if you can measure center to center distance between the existing fan screws that would help. It likely was designed for an off the shelf fan.
@Aurea ok approximate (brute force) design on a napkin, here we go: The junction voltage drop will be about 1.2 volts, we don’t know the junction thermal resistance so we will use 1.4 volt drop to be conservative. Further, let’s assume 15 amps max load and the fan contributes 10 watts (fan needs to cool itself controller produces heat this is a very conservative high guess) and performance is derated by 60% of free air blowing into a case. So lots of very conservative assumptions for our napkin calc.
Total wattage = (1.4 x 15 A)+ 10w = 31 watts, convert to btuh => 31 x 3.41 = 105 btuh.  So if we assume an expected 20 degree temperature difference, derate that by 5 degrees for fan heat  (super conservative here and double dipping) we get:
cfm = 105 btuh/ (1.08x15) ~ 7 cfm. Very small!  So the picture looks like a 60 mm fan comparing it to the size of the SSR, the fan below seems to be more than enough, is ball bearing and 240v. Install inside blowing in, wire to the terminals where power comes in so whenever plugged in the fan turns on.
The important part will be the SSR to metal connection. A bit of thermal grease and a snug fit to the metal case will remove heat from the solid state junction best. 
Ok I think we were super conservative with our loads and assumptions maybe someone here can check my math but this ought to be double the air necessary.
If I guessed wrong at the spacing of those existing fan screws, you will need to order the right size. At this airflow requirement most should work. Double ball bearings a nice feature for longevity and most important operates on 240volts ac

Yes, you likely match the 240v split phase grid standard in North America and 3000 watts ought to be just short of 13 amps so most relays ought to perform just fine. Please post pictures of the relay (s) making sure the part number and ratings printed on the relay are visible in the picture. Post any picture of a failed relay you may have as well. Post a picture of the relay mounted in place as well. Relays fail from contact overload, and also often because of overheating. So one thing folks will look at is where are these mounted in the cabinet and how are they kept cool. Blocked air inlet / discharge louvers sometimes contribute to the overheating. So context and clarity of the photos you post will be important.

Thanks for the pictures! Best guess here is this is overheating. Solid state relays (SSR) depend on cooling. So the thing I notice most is a fan guard but no fan. If installing an SSR without a heat sink then the device must be derated significantly. I have added some design curves below to show that once these things exceed 40c (104f - pretty much body temperature) they need to be significantly derated. Most of them heat about 1 degree C per amp which almost always means for this size device which depends on the backplate for all cooling they can only tolerate 7-8 amps without being mounted to a real heat sink. Cooling them always depends on the temperature of the ambient air as well so using cool air will help this significantly.
The 40 amp SSR appears to have lasted longer than the 25 amp SSR but still heated beyond its derated value. The extra rating is great but since the backplate is a certain size it only failed at a higher temperature. It looks like this is designed to be fan cooled so I think I would install a new 40 amp and set up a fan temporarily to cool the SSR and retest while measuring the temperature of the SSR with a non contact infrared thermometer to confirm.
My best guess for now, but minimal cooling appears designed into this to save money. The time limits in the literature are probably closer to being correct - just thermal restrictions on the SSR.
Some charts below and a quick blurb of how this can be designed just as an FYI of how severely these derate without real cooling. A guess would be you are currently operating around the yellow line on the graph. Set up a temp fan, confirm with infrared and once confirmed get a decent fan installed behind the guard. Blow air into the cabinet rather than suck it out. More air molecules, more cooling. All an educated guess though from the pictures.

Yep! If you have an infrared handy takes some readings and figure where it stabilizes above ambient temp with the fan. Just to mention - the SSR should be bolted to the metal with thermal paste between it and the metal. The fan will cool the SSR and the metal. That’s a nice fan and nice test to verify it works. My hope was the graphs will give you a better perspective of the actual heat sensitivity leading to a decent solution.

Yes, you likely match the 240v split phase grid standard in North America and 3000 watts ought to be just short of 13 amps so most relays ought to perform just fine. Please post pictures of the relay (s) making sure the part number and ratings printed on the relay are visible in the picture. Post any picture of a failed relay you may have as well. Post a picture of the relay mounted in place as well. Relays fail from contact overload, and also often because of overheating. So one thing folks will look at is where are these mounted in the cabinet and how are they kept cool. Blocked air inlet / discharge louvers sometimes contribute to the overheating. So context and clarity of the photos you post will be important.

I'll fire some chips in the bisque kiln this weekend.  If it is tannins they should burn out.  This is also city water, not well water, so I expect only low levels of tannins.

Tannins (fermented organics) for well water quite often assumed as Iron. Common test often included in well water test kits.

You absolutely need the insulator to keep the live electric from touching anything metal. The only way I have been able to fix something like that (temporary fix) is to torch the end of the element and unwind it while red hot to restore enough of a pigtail. Careful unwinding and torch work keeping the areas being worked red hot can get you a single or double strand pigtail without shattering your element to pieces. This is usually a temporary fix, not forever, as the resistance of this element will be slightly lower. I always tell folks to plan on new elements in the near future - most have not and just fired until next replacement.

This is the way I learned this particular pinhole theory but to my knowledge and what I have been taught, like fired COE,  the fired characteristics cannot be obtained from the glaze formulation and measuring at temperature for just one composition has its own complications.
+ one from me realizing kilns generally don’t have powered cooling cycles so they cool at their rate (thermal mass being significant here) and you simply establish holds along the way. Multiple holds can give you step control though so closer to a defined rate of cooling. To my knowledge alleviating the surface tension issue involves trial and error though. Some of the randomness to multiple trials could be the different natural rates that things are actually cooling. So if your kiln cools very quickly at top end, then your holds could be more material and reliable.
Hopefully I am wrong and someone here has the magic, but from my experience testing is necessary. Pinholes can have other causes though so you may want to explore those cures as well.
I will add that temperature differences from shelf to ware or outside of a ware to inside of an open shape always seemed highly unlikely just because ceramic conducts heat pretty quickly, generally much faster than typical heating and cooling rates it is subjected to. Still, if you find a solution based in that theory then it works for you.
I believe you need to test to find the best answer for a glaze combination. One solution I really liked was to fire short of peak temp using a hold to still make cone heatwork and doing a drop and hold from there. In my experience glazes can pinhole more so at higher firing temps. So firing one cone lower with a fifteen to 20 minute hold drives the heatwork to the desired cone but without the peak temperature. Something maybe worth trying with your established drop and hold from there.
Finally, if this reads crazy complicated, it’s just me not being able to adequately simplify, someone likely will have a simple fix.

Ceramic Shop lists this part: SBCBWHA
From Clay Planet website:
 "14” wheel head with sturdy steel structure and long lasting polypropolene[sic] composite surface "

Is the wheel head metal (usually aluminum) or a composite? My old CI wheel has a composite head and there is no way I would take a heat gun or torch to it. 

Folks;
Thanks for the continued interest and help during my quest for a Cone 10 firing! Mark it really helps to know that my burners are fixed (non adjustable) so that I can take that issue off my list of possible adjustments. I had read that some venturi burners are just designed to be efficient over a certain range of pressures, so it sounds like that is the case with my own little mystery kiln. 
Bill thanks for the nice illustrations of the burner flame and combustion tables. I will pay attention to the burner flame color as it enters the bottom of the kiln, that will give me a direct observation to indicate whether or not I have sufficient oxygen from the venturi effect, or if I am pushing unburned gas into the kiln. My understanding is that for any given damper setting, there should be a gas pressure that results in a good blue flame. More gas would then lead to excess fuel and a yellow flame? So is observing flame color at the burner a practical way to determine the max efficient gas flow into the kiln?
David, I appreciate your artistic skills! I won't try to compete with my own drawing, but my shelves are evenly stacked with the first layer 3" above the kiln floor to create mixing box for incoming flames. Total interior height is about 27", so shelf spacing looks like (from bottom to top)
3" (from kiln bottom)
6"
6"
4" 
which leaves about 6" space to the bottom of the kiln lid. The idea of placing a last shelf a few inches from the lid makes sense - it would certainly reduce heat loss from that vent, good suggestion.
In answer to the comments about my shelves, I am trying to keep it simple for now. I have > 1" space all around, and left a 1" gap in between shelves at each level. I didn't try to get fancy with staggered shelves, or with placing some shelves closer to the wall to block direct gas flow up the inner sides of the kiln. I've read about all kinds of creative shelf placement to block/channel/slow down the gas and force more mixing, but I wanted to master the basic kiln behavior before I got too creative with shelf placement.
I remain intrigued with the idea of adding a short flue to get some buoyancy effects and increase the draw of air int the bottom. However, I am going to bet that the kiln was designed to make Cone 10, if I am smart about the gas pressure/damper combination. I have to believe that I can squeeze another 80-100 F temp increase out of the kiln if I play with the gas/damper settings, as everyone is suggesting!
It may be friday before I get off work early enough to give this another shot. I want to start early enough that I won't be out there at midnight (again) trying to entice the kiln to get to 2300!
Thanks everyone!
 

Never ever lost my patience …………… er sort of - I have also had luck when drilling to get a left hand drill bit for extra special frustrating  occasion to stack the odds in my favor.

Hope you can get the set screws loosened/removed without damaging the threaded holes.
A drop of LiquidWrench might help - it dissolves rust/oxidation.
We've used heat to loosen threaded fasteners*; warming the surrounding metal  causes it to expand.
Tap-tap, some light percussion - a hammer*** - can help loosen the oxidation/rust.
Repeat the heat, the taps, the time while the LiquidWrench soak in thar...
Stubborn/broken threaded bits sometimes respond well to screw extractor type tools. I've had better luck with the straight tapers, e.g.

over the spiral type.
Be careful to drill the stuck part without damaging the threads in the surrounding material(s)!
Added: if the threads are damaged, "chasing" the hole with a tap might save it, else, if there's room to drill it out and cut new threads to the next largest size - that could save it.
 
*One must be very careful when using heat!
Not burning oneself, others, the shop, its furnishings and tools, check.
Add: beware generating fumes; beware changing the surrounding metal's temper; beware cooking any seal, bearing, grease, paint, etc.
***Tap-tap! Careful there, so easy to allow frustration to boil over and over-hit, heh.

Another technique some use  for later is to mix up a copper red glaze for reduction and place samples throughout the kiln to see just how well you reduce and maintain it. This oxblood color goes ugly green / grey pretty quickly with any sneaky oxygen infiltration. It teaches the importance of keeping the kiln in full reduction top to bottom while providing a way to map the reduction performance within the kiln. Only a handful of metals are significantly affected by reduction btw.
 

Hi again Neil, Mark, Bill,
Thank you all for your advise with my Duncan Kiln situation.  We have discovered that the LT 3K Dawson Control Panel/sitter is not old, and need replacing.  I have a new thought... the actual Kiln body is in great shape [bricks, coils, top, etc.].  I have contacted Skutt Corp. Technical Dept. about the possibility of replacing the entire control unit with their new, Skutt Kilnmaster Touch Screen controller.  They have videos on their website explaining retrofitting that unit to non Skutt Kilns.  IF that were possible [I havent heard from them yet] it would be a very cost-effective way to have a virtually new and safe kiln. I paid $400.00 for the Duncan Kiln with the Dawson Controller. The Skutt Touch Screen unit is about $600.00.
We have a friend with that Skutt Touchscreen and [attached to a new Skutt Kiln] she raves about it.  Any thoughts still appreciated!
Fred
ps:  I've attached 2 photos of the insides of the kiln...

In my experience, self-supporting cones can stick to the shelf if you overfire them just a little. They’re not supposed to, but it happens! As @Bill Kielb said, if you kiln wash your shelves, this is not a problem. I do not kiln wash my shelves, so I have had to chisel off some stuck cone bits. 
My solution to this is to use cone plaques, the kind that have holes in one side for holding non-self-supporting cones at the correct angle. I use the underside that doesn’t have holes, put kiln wash on that surface, and place my self-supporting cones on them. Any small piece of old or broken kiln furniture will work too.
 

We call that color ‘snot red 

Another technique some use  for later is to mix up a copper red glaze for reduction and place samples throughout the kiln to see just how well you reduce and maintain it. This oxblood color goes ugly green / grey pretty quickly with any sneaky oxygen infiltration. It teaches the importance of keeping the kiln in full reduction top to bottom while providing a way to map the reduction performance within the kiln. Only a handful of metals are significantly affected by reduction btw.
 

A thought I’ll share: As soon as I get the powder into the water bucket I put the lid on and go do something else for a while. It lets things get hydrated before mixing, but mostly I do it to reduce dust in the air. 

Not sure if this helps but at some point I got a Brent schematic from someone here which clearly shows .7 m  double shafted pot for the pedal and a mysterious trim pot  going into a voltage divider. Definitely not your pot but .7 M  the value is interesting if they stuck with the diac control.

Thanks! Your maintenance manual here https://aakilns.com.au/pdf/Duncan_Kiln_Service_Manual.pdf but if you have never fired a manual kiln, there are some steps to learn and detailed in the operating manual below.
This is a 24 amp kiln and the manufacture specifies 30 amp breaker, 40 amps is too large per the manufacture and North American Code.so this should really be protected with a 30 amp breaker Page 58 of 75 in the maintenance manual, bottom right corner of the electrical drawing show amperage, wire size and breaker 
This is a manual kiln that requires the safety countdown timer be set for some period greater than the time it will take to fire. So if the firing is expected to take 8 hours, the timer must be set to something greater such as 9 hours. It is for safety and if it is on or reaches zero your kiln will shut off. Did you set the timer for something greater than zero when you tested? The kiln sitter to be activated  using an appropriate cone and then arming it by depressing the plunger  Page 7 and Page 28 -33 Did you place a cone in the sittter and depress the plunger? Finally the two knobs are turned up gradually throughout the firing (they are know as infinite switches )such as two hours on low, two hours on medium and finally to high until the kiln sitter shuts off the kiln. Page 21 - 24 The manual above provides maintenance for all the components, operating this kiln is better described here https://eadn-wc04-7751283.nxedge.io/wp-content/uploads/LX851_Duncan_Energy_Saver_Owner_Manual.pdf
Last note, this kiln is rated to cone 8 if firing to cone 6 routinely you will get a moderate number of cone 6 firings before the elements will need replacement. Cone 10 rated kilns provide considerably more firings before element replacement when routinely fired to cone 6. The maintenance manual has element resistance measurements listed. If the elements have risen by 10% in resistance, it’s time for replacement to make cone 6 temperatures.