Humidity Levels - Need Help

[Bokeeliachick]

My daughter's teacher has a hovabator 1583.
She purchased it new last year.
Used it twice very successfully.
This year, we can not keep the humidity constant.
Goes down to 20, up to 70.
What could be causing this?
Any ideas or suggestion?
Thanks!

 

[chicmom]

Do you have a hygrometer, and if it takes batteries, are they fresh batteries? (That's the first, easiest thing to consider.)