Specifically this error code means that during a cooling segment in the programmed firing, one of the thermocouple temperatures is more than 50 degrees above the set point for longer than 18 seconds.
In other words, the kiln is cooling off. The programmed rate of cooling is lets say 400 degrees F per hour. This is the rate of descent that the set point will travel as it moves through the program.
The DynaTrol tries to get the thermocouple readings to follow the set point. It does this by turning the different kiln sections on or off.
There is a limitation to how quickly the kiln can respond to a change in the set point’s behavior. Normally this does not matter, but during a controlled cool down, if the set point cools faster than the natural rate of the kiln cooling, it can be enough to set off the E- 4 (E-4).
Typically E- 4 (E-4) will be seen by glass artists, or by people using a two step slow cooling for pottery.
Glass artists typically crash cool their kilns from anywhere between about 1250°F to 1480°F, down to about 1000F. Some of them even use protective gear and lift the lid to dump heat even faster. At around 1000°F they begin a very slow cool down for the annealing process to toughen the glass. Often in their program they will set the rate of cooling to 9999. This is much faster than the kiln can ever cool off so often the set point is more than 50 degrees away from the thermocouple temperatures, and the E- 4 (E-4) error becomes more and more likely to see.
Same thing with the potters using the two step slow cooling. The first step is a fast uncontrolled cooling from the top temperature down to about 1950°F. Then they slow cool it at 100°F to 150°F per hour down to 1200°F. They will sometimes set the rate of cooling from the top temp to 1950°F at 9999 degrees F per hour. The same thing happens that happens with the glass artists and E- 4 (E-4) becomes more and more possible to see.
To keep E- 4 (E-4) from appearing, program in a slower rate of cooling. The kiln initially cools naturally at anywhere around 400 – 500 degrees F per hour so if you set it closer to that rate you will probably not see E- 4 (E-4)… unless something else is causing it.
A thermocouple that is about to fail can cause E- 4, as could an intermittently sticking relay. Good news is that either one of these conditions will not stay that way for very long. The thermocouple will soon fail completely, as will the relay, and then it will be obvious what was causing the problem.
Other things that can cause E- 4 (E-4) are loose or overheated thermocouple wires or thermocouple connections. A poor connection in a thermocouple circuit will cause an intermittently higher reading. If the faulty thermocouple reading remains for more than the 18 seconds, E- 4 (E-4) will appear.
How the kiln is loaded can produce E- 4 (E-4) during a cool-down as well. When everything is loaded into the bottom of the kiln and the top is more or less empty, the rate of cooling in those zones will be quite a bit different. If their temperatures get far enough apart it is possible to get E- 4 (E-4) due to how far the bottom temperature would be from the set point compared to the top temperature. While the kiln is cooling off the area without a lot of mass will be cooling more quickly while the area with a lot of mass will cool more slowly. E- 4 is possible when the program set-point reaches 1900 and the heavily loaded area may still be 50 degrees hotter than that.
Something touching or close to touching a thermocouple would make the kiln act the same way.