I have a Scale setup with several pools, but for some reason the system no longer wants to boot (motherboard I suspect), I took 16 SATA disks off it, and using the same controller in another Scale “box”, the pool imported with no issue, so then I took 16 SAS drives, and did the same swap only to not have the Pool available at the “Import Pool” option, and trying to use Shell “zpool import” didn’t work either, stating that zpool was not a command.
If I start the “create new pool” it shows that the available disks are part of the pool I want to import, but that’s all I can do 
Any suggestions will be very welcome.
Thanks
sudo zpool import
Hello and welcome to the forums.
Could you have created this pool on a newer version of TrueNAS which your existing version doesn’t support certain features? As @NugentS said zpool import should tell you if this is the case.
If so the fix is to update your version of TrueNAS.