Sonoff TH16 + Temperature sensor values

Hello everyone!

I am using Sonoff TH16 + temperature sensor in order to see my water heater temperature.

The issue i face is that it at random times (1 time / 2-3 days) reads fake temperature and the history is no good.

Maybe the issue is caused by the cable of the sensor (witch about 15meters).

I have tried to use filers (range, outlier and lowpass) without much success.

Witch is the best way to have right history? Is there any way not to include values witch has difference bigger than 20 of the last one?