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Sondahl's Guide to Home Electric Kiln Repair

Electric kilns consist of:

An outer shell of stainless steel
Channeled insulating brick with peephole plugs
Lid and bottom of kiln and support.
A power supply cable, hooked to an electric circuit breaker
A means to turn up power incrementally  and shut off power when the kiln is finished
Then there are the elements themselves...
Cheap Electric Kiln exhaust

Each of these is discussed on this page.  To quickly access a specific part, click on the links.

Remember to disconnect the power to the kiln before accessing any of its electrical parts, including elements.  The opinions I express on this page represent my own practices, presented for discussion purposes only.  If you follow any of the advice given here, you assume responsibility for your own actions.
For advice on specific kilns, contact the manufacturer.


An outer shell of stainless steel
This shell holds the firebrick in place, and should last longer than the rest of the kiln.  However it is attached at the ends usually with screw type hose clamps, and these tend to rust out, or at least the sheetmetal screws holding them. If you see this happening, buy some new hose clamps, cut them in half with heavy tin snips, drill holes in the two halves near the ends for sheet meal screws, drill new pilot holes for the screws, and attach the replacements.  Tighten when finished.



Channeled insulating brick with peephole plugs
This firebrick holds the elements in and provides insulation for the kiln.  The main problem with it is that chunks of the brick fall off with time, particularly when elements swell after long use, and take out chunks of brick as they are removed for replacement.  Generally, once a piece has come loose it does little good to try to reattach it.  The parts that come loose are invariably outer pieces of the channel which support the elements.  The elements, once freed, start to stretch when red hot, and if they contact their neighbors, can arc and ruin both elements.   To avoid this I use staples made from heavy Kanthal element wire (the wire is usually available from pottery suppliers).   These staples are just U shaped bent pieces of the wire, bent with a needle nose pliers, starting with a piece about 2 inches long. The pliers can be used to force the staple into the soft brick of the kiln, securing the element in place.  It may help to have put them in slightly at a downward angle, so that gravity will help hold them in place.

Peephole plugs:
These crack and break from thermal stress.  You can make your own by mixing a small batch of pure clay (kaolin, ball clay, EPK, and or fireclay) and water, with sawdust in it to give it air space.  After mixing, shape the plug by hand into a cone shape approximating the size of the hole on the kiln.  Allow for shrinkage.  Dry thoroughly and fire in your highest normal firing before use.  If you use sawdust, expect smoke as  the peephole heats up.



Lid and bottom of kiln and support.
The lid of the kiln tends to develop cracks with age.  To some extent this can be avoided by maintaining sufficient tension on the lid, with the screw type hoseclamps used to secure the steel flange around the outside.  This flange is critical in supplying support for the lid--if it were to become detached, catastrophic failure may result.   These hose clamps and the sheetmetal screws used to attach them can become rusted with age, and can be replaced as necessary (instructions).  If chunks of insulating material are falling out of the lid, or any sag is detected in it, or wide cracks are appearing, replace the lid. Even though the bottom supports the whole kiln, it is not stressed as much as the lid, which is opened and shut frequently, so the bottom will likely last longer than the top.  But another concern is the base which holds the whole kiln.  Sometimes this is not made of stainless steel, and if not, it can rust out. Check for rust on your base.  If necessary the kiln can be set on regular masonry bricks or probably cement blocks, preferably with some space to allow heat to dissipate into the air.



The power supply cable and circuit breaker.
These are both possible causes of frustration for the kiln user.  As the cable ages, it can build up corrosion where it plugs in, and if the corrosion is thick enough, it can cause the plug to arc.  Since kilns are designed to draw a lot of amperage, this situation will not necessarily trip the breaker.  The closest I've come to a fire from my business was when my plug in connector arced and started burning the plastic housing for the receptacle.  My kids noticed it and I shut off the power and extinguished the fire before the wood wall caught.  Since then I always hard wire the kiln with screw type connectors inside a junction box. Kilns don't need to be that portable...  You may want an electrician if you want to do this.
The circuit breaker can become a problem, if it starts shutting off during a firing.  If you have this problem from the beginning, you probably need a bigger breaker.  But breakers are matched sometimes to wire size, so make sure your wiring can handle a bigger breaker. Also make sure you check your elements for arcing before the expensive step of a larger breaker.  And as breakers age they can start shutting down with lower amperage, so that may be grounds for replacing also.  Remember that you should probably not exceed the recommendations of your kiln provider, as too large a breaker may promote dangerous arcing and potential fires.



Switches and shut off


For most of my career I didn't use a computer controller.  I did use a thermocouple shut off system from Seattle Pottery (they no longer offer it), but it cost about $30 per year for thermocouples, and finally the electronics burned out.    I recommended the  Kilnsitter (was Dawson, now Orton)  with timer as the simplest, cheapest, and most dependable way to shut off your kiln.  This means turning up your power manually--which most of us are capable of.  The kiln sitter can need new metal posts which support the cones, a new porcelain tube assembly, or new contact block in the switch.  Also if the spring that makes the button lock on gets rusty or weak, the button will get very tempermental and not stay in... If you need advice on repairing these, email me or talk to your supplier.  (update, 2012...  I finally gave up on kilnsitters when the button got arc welded in the on position during a firning twice this summer.  I suspected flawed materials used for the kiln contacts, but had to bite the bullet for new kilns.  Because I suspected the contacts, I finally tried using a Bartlett controller, which is digitally controlled and uses relays turning off and on to guide the kiln up in a proper firing curve.  Since switching, I've become a believer, with it speeding up firings and producing predictable results.  I did have to replace one of the relays after 40 firings, covered by warranty).
Getting back to if you have a kilnsitter: The manual switches are usually either 3 position(low, medium, or high)  or infinite (no click setting from low to high). I have had kilns with both styles.  Infinite switches can sometimes be recycled from old electric stoves.  3 position switches can handle more amperage, so you get by with fewer of them, and are generally more reliable than infinite switches.  With either of them I turn kilns up just three times, every two hours of the firing until they are on high.

If a switch burns out, usually there will be a post that is wiggly, or something will rattle when it is shaken.  Whatever wire is connected to that burned post needs a new connector crimped on, to prevent damage to the new switch.  The wire itself may need replacement--if so, contact your pottery supplier, as this is special high temperature wire.  You replace the switch by shutting off power at the breaker,  removing the knob, loosening the large nut under the knob, and moving the wires to the new switch.  It's generally easier to reattach the wires before sticking the knob on again.

If the button that starts the Kilnsitter going gets fussy, and refuses to stay in, here are some tips:
Assuming you have remembered to put time on the knob for the kiln timer, here are other possible fixes:  You don't say how old the kiln is, but the wire spring that makes the button stay in place while firing can get rusty and catch on the back of the black plate that is the front of the kiln sitter.  Sometimes you can squirt some WD-40 in from the side and that will help for a while (make sure to let it evaporate before attempting to fire the kiln. )
 The more permanent solution I've found recently involves (with electricity to the kiln SHUT OFF at breaker)  removing the 4 screws at the corner of the face plate, and pulling the kiln sitter out far enough that a piece of heavy nylon fishing line can be poked in from one side to the other on the back side of the plate, below the button area.  When it comes out the other side, poke it back through to the beginning side, making sure to loop it over the thin straight wire spring which should be visible just below the thing that flops down to shut the kiln off.  When it comes back through, grab the two ends of the fishline and tie them in a simple overhand knot so it's a closed loop circle, hanging out a few inches towards the front of the kiln.  Now you can push in the button, while gently pulling on the loop, which will give the spring some added oomph. 



Elements
Elements will last until they burn out, but their efficiency goes down with the number of firings (particularly high fires) they have done.  To check elements, turn on the kiln to high for a couple minutes.  Shut off the power, and drip a bit of water on each element.  The hissing tells you which ones are working.  If they are not heating  inspect the element for an obvious gap or break. If this does not work, run a small screwdriver or your fingernail along the whole route of the element, checking for gaps or burnout holes. If you still haven't found a problem, or if two elements on the same switch are not working, suspect the switch (it's sometimes easiest to replace the switch rather than test it.)  A continuity tester can be used also to see if the element has continuity throughout its length.
If you do find a burned out section of element, remember to put kilnwash over it before putting in the new element.  This will prevent a hastened repeat burnout, caused by the metal residue which still conducts some electricity.
    If you want to roll your own elements or buy premade ones: Duralite still sells the bare Kanthal A-1 wire. Duralite in Connecticut custom rolls elements (860-379-3113).  I ordered two pounds. That will make, as I recall, about 6 elements for my old Crusader kiln . If you send them all the pieces of your old element, they will size and price it for what they would make, or tell you what how long to make yours. Then it's a question of using a rod the right length, and winding the wire on compactly. Duralite has for the asking a photocopy of info on resistance per foot per gauge of wire, etc. I've used a  welded crank and steel rod (with a slot cut in the end to hook the wire in to start. Lately I've used a variable speed drill with rod stuck through a hole in mounted wood to stabilize it. It would help to have one person run the drill and another to guide the wire. The ends are fairly easy if you use loop ends-- tougher if they're supposed to be just tight twists.
    When you're ready to put in the new elements, clean the channel thoroughly of bits of old element and dust.  A lot of kilns use little pins in each corner to hold the element in place.  I don't like them much--most elements come sagging out of the middle flat areas, not the corners.  I just use them in problem areas (see insulating brick repair)


Cheap Electric Kiln exhaust
I once added a cheap kiln vent to my electric kiln.  I bought some flexible aluminum clothes dryer vent and attached it to the bottom peephole of my kiln with three sheetmetal screws with added washers to keep from ripping through the thin metal.  At the other end of the flexible section I used standard rigid aluminum dryer vent tubing to get it out of a window.  Outside I added a small fan mounted in an A-frame of plywood (so as to protect it from rain/snow).  From inside I can push the vent tube closer to the fan to create more suction, or farther from it for less.  When I fire a bisque, I want more suction, to vent the sulphur fumes.  You can tell how effective the venting is by how hot the pipe is getting.  It never seems to get too hot to touch.  No longer the taste of sulphur when I fire...   Do bear in mind that in venting out fumes, you are also removing some air from the room, which must be replaced somehow.  If you are in a confined area with fuel fired appliances (gas hot water, furnace, or woodstove), the draft created by drawing out kiln gases can also draw into the room some of the exhaust gases from these other appliances, including carbon monoxide.  So you may need to run a vent hose into the kiln space to equalize pressure.  Also, using aluminum piping is better than steel stovepipe, as the aluminum resists rusting out...

The following are related pages on my website:

For a large list of original Sondahl Pottery glazes (Cone 8-10 Oxidation), click here
Sondahl's short guide to crystalline glazes
Collection of my Ceramics Monthly Articles and other pottery thoughts
Multiply your glaze tests with my Glaze Hybridization system page
Offsite related links:
 http://www.euclids.com/  Another supplier of elements and kiln info
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