Random, rapid BCS temp probe swing after 6 months? HELP!

Hi guys,

My fermentor temperature probe (for BCS) has worked without fail since I purchased it back in June 2013. All my probes were purchased from Brewers Hardware.

I had been using a ceramic space heater in my chest freezer to maintain fermentation temps around 68 to let my two beers finish up after 1.5 weeks of fermentation. Everything looked good until the "heat mode" kicked off. If you look at the attached photo, you will see the black line (ferm temp probe) jump all over the place over the past day or so (up to 70s, down to 60s). It should be reading closer to 50F (ambient temp).

To try to troubleshoot, I placed the fermentor probe, another probe (usually used for my MLT), and a thermapen into a bottle of water. The MLT probe and themapen are relatively close at ~50F while the fermentor probe is reading 72F. I even tried switching the probe inputs (the cat5e's) and it flopped the temperature readings, indicating that it is isolated to the temperature probe/sensor and not my BCS/control panel wiring.

Is there some reason that could have triggered it jumping way up like this? Have you ever experienced this before? Do I need to recalibrate the probes? Is my ferm probe trash? Any ideas?

Any insight would be much appreciated. Thanks!

Might there be some condensation that got inside the probe's shell? That could change the resistance values quite a bit.

If that is the case I've got two questions then:

1. How do I reseal the probe/wire interface to prevent more condensation from entering?
2. Do I have to do the 3 point calibration as described on the BCS wiki or can I just calibrate from one single point?