Hi, we are happy to hear that you have a ProfiLux Plus II (upgraded to 3) which must be at least 6 years old and it is still working great besides this temp. issue.

Maybe during the last couple years the electronics and/or the temp.-probe aged a bit. I think it is possible that the temp.-sensor is defective, maybe even the PII-board, maybe even caused by external circumstances.

I think it is worth to try a new probe.