Communication Failures will sometimes arise if you have 2 or more weather sensors of the same type and with the same channel selected. One or two sensors are sometimes not received for a few hours. The reason is that they transmit during this period on the same moment. The interval time differs a very little bit for each sensor and the transmit period shifts slowly and at a certain time both sensors transmit on a different time again and are received again.
The solution is to select another channel on each sensor of the same type or use different sensor types.
Note: TEMP1, TEMP2 are different types but THR128 and THC138 are the same types as they are both TEMP1 sensors!
The THGR810 is a 10 channel sensor and you can use 10 of these sensors without having the Communication Failure due to sensor transmission overlap.
If different channels are selected or different types are used and communication failures occur an out of range is the most expected problem. Don’t install the sensors near metal objects because this can limit the range too.
It can still happen that sensors transmit at the same time when having different sensor types or different channels selected but not for a long period and Communication Failures will not appear due to this.
For the list of supported weather sensor types see: http://www.rfxcom.com/oregon