Hi Carmalee ................. I'm guessing, but, if the bathroom rad is the ONLY one with no thermostatic valve, then it's probably the "heat leak" rad.
Don't adjust it. Certainly don't turn it off.
It's there for the unlikely, but possible occurrence when the boiler is hot, but all the TRVs (thermo rad valves) have closed. The heat has to go somewhere for boiler safety, so one rad with no TRV dissipates all the excess heat.
That's why the bath rad is hotter. Upstairs, you could most likely turn off all the other rads, leave all the doors wide open, and let this rad take care of upstairs on its own.
If you're worried about cost (really not that much) ......... turn the boiler heating temp down a bit just for while you're away.