Hi Jakub,
yes, it sounds like that the remanent memory is not configured, this could be the problem (I’m almost sure it is 
).
To use remanent variables, you need a PLC with SRAM (Static RAM → most of the PLCs have SRAM, either directly onboard or, in case of a PC based runtime system, on a interface card plugged into the system).
Because I don’t know which PLC you use, I can’t tell you exactly what to setup, but I can give you a example with a X20 PLC.
The memory setup is done inside the PLC configuration, under “RemMem” and “PV memory”.
Depending on the PLC type, maybe you have to change the settings at “Device for memory RemMem” → without changing anything else, there should be then a value != 0 under “RemMem memory size” (this value can also be changed, but normally it’s ok to leave the predefined default value).
After that, if you have GLOBAL variables that should be remanent, you have to set a suitable value at “Remanent global PVs”. The value unter “Remanent local PVs” is calculated automatically and is used for local variables declared as remanent.
More information about the SRAM memory configuration can be found here in the online help.