Good morning, this is not normal (if it smells like burning).
However if its not been used it may just be dusty and as its heating up burning the dust, the smell should dissipate after 6 hours of running I would expect, if it doesnt I would be inclined to give it a good dust from behind.
Is the TVR hot to touch, as the valve itself is metal its only the plastic on top made of plastic.
I would be inclined to think its due to you having a higher flow rate where you have reopened the balance valve on the other side.
Is the TRV top hot to the touch?
I would start by turning down the radiator balance valve on the other side of the TRV, and have it set so its 1/4 open, air the room and see if after an hour if the smell is still present.
You could also close the TRV so its on frost protection, and see if the smell goes, then I would look to clean the radiator with a duster to remove and dust at the rear.
Sounds like its just the oils drying out on the radiator cover, this isnt giving off dangerous fumes I would just place them in the airing cupboard or somewhere warm for it to air and dry out.
In conclusion I dont think you have anything to worry about, and do not think this is a TRV related issue.
Appreciate if you can rate the service received so I may resolve the case.