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F2, F3 Temperature Sensor Error Codes. Replaced Sensor, Replaced/Repaired Board - Problem Remains.

Temperature sensing...

might be the most critical aspect of oven control.  A bad sensor or bad sensing circuit can cause a few different of problems: 

  • Oven does not get to set/target temperature

  • Oven overshoots set/target temperature

  • Oven heats inconsistently

  • F2 or F3 error codes, oven does not heat

The first thing most appliance technicians and DIYers will do when they encounter any of these symptoms is inspect the temperature sensor.  A typical temperature sensor should read 1000-1100 ohms at room temperature.  Even after confirming that reading, many still replace the sensor in an effort to eliminate the problem.  If replacing the sensor doesn't work, the next step is replacing the control board.  If a new board isn't available, then it can be repaired.

What do you do when you still have those symptoms after confirming the sensor and the board are good?

 

The answer lies in the wiring from the sensor to the board.  Since the temperature sensor is sticking out into the oven cavity, it can get pretty hot. The wires that attach to the sensor need to be able to withstand the high temperatures of the oven cavity.  But the control board is not as exposed to high temperatures, so the wires that attach to the control board do not need to have the same resilience.  Rather than using expensive heat resistant wiring for the entire span from the temperature sensor to the control board (which usually means wrapping all the way around the oven several feet), manufacturers keep costs low by only using the heat resistant wiring for a few inches immediately after the temperature sensor, and then splice the connection to normal wiring for the remaining length to the control board.

The spliced connection is typically joined by wire nuts, and these connections are notorious for getting rusty or corroded.  A corroded wire connection will become electrically resistive when energy is in the system, but when the system is in a low energy state, the resistance is normal.  This means that when someone measures the resistance of the temperature sensor at the wiring harness on the board while the oven is off, they will get a normal resistance reading.  And if you measure the resistance of the sensor at the sensor, you will get a normal reading as well.  It's a really difficult problem to troubleshoot, and you basically just have to assume that a wire nut connection is bad if you find yourself in this scenario.

Rusty, Corroded Wire Nut Splice Connections

It's an easy fix, though, once you've located the spliced connection.  The best fix is to cut out the existing connection, strip away fresh wiring insulation and splice the wires again.  But if you don't have wire strippers or don't feel comfortable doing something like that, then you can try spraying the exposed copper of the spliced wiring with contact cleaner or WD40 to clean off the corrosion.

And voila! The oven works like new again.

 

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