Before I had an adapter on my HR24-500 I use the ethernet too. The only way to switch from ethernet back to coax was to remove power form the STB for several minutes, then restart it with the coax only connect (removing the ethernet before applying power; audio video connections can be made). Once I did that it came to coax. Out of curiosity, what does your wiring map look like for RF and the DECA?
I unplugged the box for 20 minutes, restarted with the coax connected, nothing. It just won't see DECA. My wiring map is:
SWiM SL-5 to SWiM 8 port splitter (all green labeled)
one output to HR24 with PI
one output to HR21-100 with DECA Adapter
one output to HR20-700 with DECA Adapter
one output to H24 no adapter.
one output to Deca/Internet adapter connected to my router
The H24, HR20, and HR21 all talk to each other and are connected to the internet. The HR24 is the only problem child.....