AO Smith 40 gal NG hot water tank internal tank temp sensor

PeteA

I was on the phone with AO Smith tech support and they were really helpful getting me a replacement gas control valve assembly for my hot water heater I installed in May of 2023. Everything went great with the install and set up and its been running like a champ but.. The internal temp sensor is either not making good contact with the well or its defective (out of calibration range) or the circuit board it's attached to is defective.
I believe this because the output of the hot water temp is significantly over the range that the documentation said it should be. At low I'm getting around 135 degrees at the faucets and at hot i'm getting up around 155 at the hot setting. I currently have it at the low setting and I installed the Caleffi tankmixer to be safe.
My question is should I just swap out the temp sensor and the circuit board when the new kit arrives or should I completely drain the tank and remove the whole unit from the tank. Is there a way to test the temp sensor with a multimeter, I figure it should have a certain resistance at certain temps but if I have the new one I would just swap it out to be safe. I figured I'd ask because I've seen the blow up diagrams of these controllers and it looks like all of these things can be accessed under the front cover relatively easily without disturbing the seal at the tank where the well goes in.
Just want to know what others do in this case since everything else seems to be working well except for the temp sensor regulating the temp based on the front of the controller markings.

EBEBRATT-Ed

I don't know what they are using for a temp sensor. If it is a capillary tube and bulb it may not be pushed into the control well all the way.

If it is an electronic sensor the same thing holds true.

With electronic sensors the mfg (don't know about AO Smith) will provide a chart where you can measure the sensors resistance and look up the corresponding temperature if it matches the sensor is good if not it is bad

PeteA

Thank @EBEBRATT-Ed that’s what I figured also. I’ll take a look at the new one when I get it and see exactly what the components look like. I believe the use the electronic one like the Bradford white water heaters and I found the ohms chart for their sensors.
i was also just curious if other folks find it better to replace the soft parts in the control assembly instead of breaking the seal in the tank by swapping out the whole unit.