Today I replaced a controller on a customer's Skutt kiln. It was the wall mounted type, but it uses the same parts as the kiln mounted systems. The controller had fried out, and there's no good way to fix them. By the time you send it off to have it repaired and pay for shipping and labor and everything else, it's faster and just as cost effective to buy a new one. Currently, a new Skutt KM circuit board with touch pad is $260. Replacing it is fairly simple, but you have to make sure to get the wires hooked up in the right order.
When controllers fail, they do all sorts of goofy things. The most common symptom that I have seen is when some of the buttons stop working, like on the controller I replaced today. The Cone Fire section of the board wouldn't work, and some of the number bottons were dead, but the Ramp/Hold section worked fine. Another common symptom is when the bottons still work, but the controller simply won't go when Start is pushed. The most difficult diagnosis I've had was on a very old controller that seemed to be working fine, but every few minutes the temperature readout would jump several hundred degrees for a few seconds, which would confuse the system and shut it down. Replacing the controller fixed the problem.
I worked on a kiln this last summer that was only two years old and was having trouble getting to temperature. It would just stall out at 2000 degrees, then shut down. Due to its age I didn't think that it was a controller problem, and the elements weren't necessarily worn enough to blame them. After changing the thermocouples and thermocouple wires the problem persisted. So I changed all the elements, still with no success. So I switched out the controller with a controller from one of my kilns and we still had the same problem. After talking with the tech at L&L Kilns, and the tech at Bartlett Instruments (they build the controllers for L&L and Skutt), we decided it was in electrical interference problem. We have no idea why this suddenly started happening to a two year old kiln, but it was fixed by adding a grounding wire to the center tap of the control board. It took a couple of weeks to get through all of it, but it's now working fine.
What makes a controller go bad? Age, moisture or an electrical surge. How do you keep your controller healthy? Keep it in a dry environment, and shut down the breaker when you're not using it. I've had several schools fry out controllers by leaving them on during the summer months, when we get a lot of electrical storms.
With minimal care and fuss, a kiln controller will last many years. But like any computer, they eventually wear out and need to be replaced.