I unplugged the cable from the router but after twenty minutes or so, the recordings started deleting. We don't have any remote DVR devices.Since it is happening on the replacement box as well, it's not the Hr54.
Disconnect the HR54 from your router (wired or wireless) and see what happens.
Do you have any active remote DVR devices?
All recordingsMakes no sense at all.
All programs or just certain ones?
Switch your remote to RF control of the HR54 instead of IR.
All. There is nothing set to auto delete recordings.How many episodes do you have set to "keep" for your series links?