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Thermador Oven Broil Element not Heating.

Model #PRSE486GLSicon, this is a rather large unit with two ovens, six burners, and a griddle, and everything was working with the exception of the broil element in the larger oven on the right. The bake functions of the larger oven seemed to work properly and the smaller oven on the left was working just fine.

Although this is a rather large example of a range, the range parts inside these ovens function much the same as any other electric range and in many cases, the larger units have components that are easier to get to. Electric elements use two 120vac circuits, one connected to each side, to make the 240vac necessary to produce the high temperatures for baking. These circuits are controlled by a control board or mechanical thermostat that will turn the voltage to one side of the element on and off based on heating demands. Voltage to the other side of the element will also be turned on and off, but by a different set of controls which only completes the circuit when in use. The reason for this is to ensure no power is present at the elements from either circuit when the oven controls are turned off. In older ovens, it was not uncommon for one of the circuits to be live anytime the oven was plugged in, causing some excitement when anyone tried to change an element with the power still connected but the oven turned off at the control. So ovens these days will open both circuits through the use of a relay or selector switch, just to be safe.

This oven has no electronic control, but instead utilizes a very accurate mechanical thermostat along with a push button type selector switch. The thermostat regulates the temperature inside the oven by turning on and off a relay under the oven which controls the L1 circuit. The selector switch on the other hand provides the L2 circuit to both of the element, and also selects the mode of operation, be it bake, broil, or clean.

Because it was only the one element not working, my first check was at the element terminals which I would expect to find my 240vac indicating both circuits are working. Unfortunately, I was only measuring 120vac which indicates one of the circuits is open. Using the wiring diagram, I started to make voltage measurements looking for the point in the circuit voltage was no longer present. What I found was voltage coming from the selector switch to the switch labeled 30AS (lower right corner of diagram) but nothing after. This switch is called a sail switch because the actuator arm is usually a metal shaped sail that is used to ensure cooling fans are operational before certain functions can be started. This range needs good air circulation during the broil and clean cycles, and switch prevents these operations unless the fan is working.

With the sail switch keeping the L2 circuit open the broil element was not going to turn on, but what was keeping the fan from working? Fortunately, the cooling fans for both ovens are easily access able without removing to many parts, and once I was able to get it in my hand, the reason became apparent. The motor wiring located on the side had been chewed on by a mouse, and now the motor was an open circuit. Without the fan blowing air, the sail switch stayed open and the broil element no longer heated. That about sums it up.

The mouse was apparently long gone according to the customer so after checking the rest of the exposed wiring for any signs of damage, I installed a new cooling fanicon to the blower mount. With power turned back on, I started a broil cycle, heard the fan come to life and the broil element began to glow shortly there after. The customer was happy to have there large oven back, and I was glad I could help.

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