Oven Temperature Sensor reading incorrectly only when installed on oven

Ok - this one has me stumped. My gas oven has been having issues heating up. I set the bake function to 350 degrees and the actual oven (measured via standalone oven thermometer) barely cracks 150 degrees. Initially I just purchased a new temp sensor off of amazon and replaced it. The issue did not resolve. Next I took off the oven control board to inspect for burnt runs/solders - everything looks good. Next I did what I should have done first and broke out the multimeter. I checked resistance of the sensor at room temperature and it read good (I think 1080 ohms). Next I set the heat to 500 degrees. The oven only got to ~150 degrees (as indicated by the standalone thermometer - the oven indicated 500 degrees was reached). I read the temperature sensor and it read out ~1900 ohms. This leads me to believe the oven control board is good and the sensor is bad. Next I removed the oven temperature sensor from the oven, put it in a pot of boiling water, and took readings... IT READ PERFECT (~1350 ohms)!!

All of the temperature sensor readings were taken at the back of the sensor itself (little white plug) so I can rule out addition of any resistance due to poor wiring/connections between the sensor plug and the oven control board. I thought the oven thermometer could be bad so I put in a dish of water and set the oven to 350 degrees. Water didn't even come close to steaming/boiling so I'm fairly certain the standalone thermometer is working correctly.

My question is this - what could cause the sensor to work fine off the oven, and then poorly when installed back on the oven? I thought maybe it had to do with the temperature range, but my oven isn't even getting as hot as boiling water (which the sensor read correctly on). I have two prevailing theories:

1. Resistance is somehow being added to the sensor via some sort of physical interference when installed on the oven. Any credence to this? I'm not the best with electronics and resistance so I really don't know.

2. The oven is installed on a GFCI outlet which is causing some sort of weird resistance readings on the sensor. This is my prevailing theory. The oven shouldn't really be on a GFCI anyway so I might try an extension cord and then rewire the GFCI if that fixes it.

Anyone experience anything similar? Thanks.

 

Welcome to the forums.

Your problem sounds like a worn igniter. The igniter is in series with the gas valve. When the igniter glows white hot it draws a certain amount of amperage and the safety gas valve opens.

Your igniter may look ok but not glowing hot enough...... I'd recommend changing it.
I've rarely come across a bad temp sensor.

 

Pete,

Thank you for your response! I am not sure it is the ignitor as the oven does in fact heat, just not to the correct temperature. The oven control board reads out a temperature of 350 degrees, when in fact an independent thermometer measures a temperature of 150 degrees. Is it possible for a temperature sensor to output a higher resistance due to a bad ignitor? The oven is not struggling to ignite - I can hear it flame up on the first click every time.

Thanks again for your help.

 

Check the resistance right at the control board.

 

Pete,

Checked resistance at the board. It's tough to read - kind of jumps all over the place and my meter's LCD screen fades in and out (just replaced the batteries on the meter). You think it could be the control board?