Electric stove burner starts and stays on high on lowest setting. Infinite switch passes ohmmeter tests

Question

BACKGROUND: I have a GE glass-top radiative stove (model jp3030tj2ww) that has 1 burner that starts on high on the lowest setting and gets stuck there and a 2nd burner that only does this sometimes when I have the heat set to level 3 (~1/2 way) or higher. These are both the large pan 2500W burners. The other two (smaller) burners work as intended.

WHAT I'VE DONE: I've taken apart the stove and inspected each of the 4 infinite switches (msa-w735-gem) with a working ohmmeter. I've tested each pairwise combination of wire tabs for continuity and for resistance (ohms) in OFF, high, and low settings according to instructions such as here.

• All 4 infinite switches performed the exact same. None had continuity in the off setting, and each registered a resistance of < 1 ohm when turned on regardless of temperature setting.

  ^{[I will note that the L1 to P reading for each fluctuated constantly/greatly from ~20-180 ohms -- however, I have no issues with the light and am not sure how to interpret this].}

STATUS AFTER TESTING: All 4 infinite switches "passed" the ohmmeter test and all behaved identically. But what gives??, since 1 supposedly doesn't work at all and another only works some of the time.

None of the contacts are stuck on any unit, and the non-working units have components that I would argue look to be in even better shape then the working units -- though, there's hardly any difference. The non-working switch lacks burn marks that I have see demonstrated on a lot of how-to videos.

MY QUESTIONS::

1. What else can I look for on these switches to indicate that the switch is to blame?*

2. I just can't image there is, but can any other stove component lead to these symptoms? (i..s, am I missing something??)

^{*Part of this is educational. I'm trying to learn more about these components, and I am really stumped as to what else could fail on the switch and how I can learn to identify it without having go the trial and error root.}

Answer 1

It's likely that your switches have gone bad and need to be replaced. I had the same problem on a similar model last year.

The way these switches work is with a bimetallic strip (similar to the way car turn signals used to work 25+ years ago). As the electric current travels through the strip, it heats the strip causing the metal to expand. Because the two pieces of metal that are joined together expand at different rates, the strip curves away, breaking contact. As it cools, it straightens, reconnecting the circuit. (If you listen carefully to your stove, you will hear the clicks as the bimetallic strip connects and disconnects the circuit.) When you adjust the dial between different heat levels, what you are actually doing is changing the size of the gap between the strip and its electrical contact, thus changing the frequency at which the heating element turns on and off.

In your case, most likely either the bimetallic strip has gotten stuck in the closed position, or the distance adjustment mechanism has failed. The switch itself cannot be easily repaired, so you will have to replace both of the malfunctioning ones. (While you have the whole thing open, you might just want to replace all four.) The reason all four switches show low resistance in your test is that the low voltage used by the ohm meter doesn't heat up the strip enough to make it bend.

Answer 2

Appliance tech here. I agree with the previous comment however

Also check the knob itself. I can’t tell you how many situations exactly like this one I’ve come across when it turned out the knob itself was broken.

It’ll come down to either the switch or the knob though.

Answer 3

The thing that makes the bimetal inside the switch move (thereby opening/closing contacts) is an internal heater strip. If the heater is burned out, or intermittent, of course the switch function will be degraded. But the other factor governing switch operation is pressure on the two flexible arms holding the main contacts. EDIT: DISREGARD: [Pressure on one side is provided by the circular ramp connected to the knob. The other "bottom" contact, on the switches I'm familiar with, is attached to an arm which is more or less exposed on the exterior of the switch, and the position of which is adjustable by means of a sheet-metal "peg" that is friction-fitted into a hole in the plastic switch body. Small movements of that peg result in large changes in heat output at the stove burner. That peg's position can clearly be altered by rough handling or accidental contact. It's clearly also a means to calibrate switch operation.] END DISREGARD. Research tells me the stove model stated is a 4-burner cooktop with ordinary (no glass top) surface resistive burners. More importantly, the switch model number stated is a parallel heater circuit switch, which means a heater element open condition will result in little or no movement of the bimetal strip holding the main contacts, and therefore continue to operate in HIGH (and possibly higher than HIGH) mode. This is in contrast to most infinite switches I've seen, which have the heating element in series with the load current path, and failure will result in no heat at all in any knob position.