It also appears that the OP is not going to have access to find the answers to many of the questions posed here either. Seems like its a "You need to get rid of that interference but we're not gonna let you touch our stuff" kind of deal. Not always productive to finding the best solution...
A quality temperature measurement instrument system properly designed should not have a problem with RF interference.
Agreed, but 20W of RF energy is sufficient for plenty of mischief.
cowboyro , thanks for the sensor (thermal probe, temperature transmitter) details.
A 2 wire current-loop over twisted pair (assuming the sensor is really wired with a single pair and not 2 wires from separate pairs) is fairly noise resistant (common mode interference).
I would try a ferrit choke to block RF and a 100nF ceramic capacitor at the controller end of the sensor cable as remedy if the interference is injected somewhere along the route of the cable between temperature transmitter and controller.
Unfortunately the OP is dealing with active electronics inside the temperature transmitter and depending on model perhaps an additional 6ft of cable for a remote temperature probe. The probe itself is just a 100Ohm thermal resistor and therefore a ferrit choke and capacitor may be used if the interference is injected at the thermal probe or cable between probe and temperature transmitter.
If the interference is taking place inside the electronics of the temperature transmitter it gets a bit more complicated. -- Got some spare cpu cycles ? Join Team Helix or Team Starfire!