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Electrical “Noise” and Digital Kilns

The digital temperature controller on today’s electric kilns is very reliable. However, occasionally something in the environment causes a controller to display unusual error codes or erratic temperatures. Here is a list of the most common causes of these errors. This list applies to all brands of digital controllers.


If your controller begins to show error codes or erratic temperatures after you move the kiln to a different location, the source of the problem is probably outside the kiln:

A loose electrical wire at the breaker box or the wall outlet

A loose grounding wire in the electric circuit

A phone line that is grounded to the electrical system

In an industrial setting, a large motor that has lost its capacitor. (This same problem causes a radio to buzz.)

Nearby arc welders


A loose or corroded wire connection inside the kiln:

Connections on the transformer

Connections on the fuse holder

Connections on the relays

Connections on the controller

Loose element connectors

Thermocouple problems:

Thermocouple lead wires that are too close to an electrical wire inside the kiln switch box, causing electromagnetic interference

A thermocouple that is shorted to the kiln case (This will cause a thermocouple failure message or make the temperature reading less accurate.)

A loose thermocouple connection, either at the lead wires or ceramic connection block

A cracked lead wire under the screw in the thermocouple connection block

A damaged thermocouple tip (Reach inside the firing chamber and wiggle the thermocouple tip. If the display makes a sizable jump in temperature, or the temperature becomes erratic, replace the thermocouple.)

Thermocouple lead wires with bare insulation that touch a grounded object

Relay problems:

A chattering or buzzing relay (A normal relay makes a clicking noise. A buzzing or chattering noise, however, is a sign that a relay is about to fail. Such a relay can cause electromagnetic interference.)

A relay with a short, which drains the power from the controller

Mercury relays that do not have MOVs (electrical “noise” reducers)


Emma Ralph, who lives in the UK, asked, "I have noticed that when ramping up my Caldera kiln slowly, I get the usual clicking noise of the relay cycling on and off, but there is also a soft buzzing noise in between. This has me worried."

Magnetism is formed when electricity passes through a coil of wire such as a heating element. Depending on where you live, AC electricity changes direction 50 to 60 times per second. When it flows in one direction, the coils attract each other. When it changes direction, they repel each other. That causes the humming noise.

You will notice that the humming lessens as the kiln gets hotter. This is because the element coils become soft and no longer vibrate.

The sound of elements humming is reassuring to me. It means that all is well and the kiln is firing normally.

Arnold Howard

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