How do you tell if cockatiels cant get in the nesting box?

All my Cockatiel nest boxes are 12 inches in height 10 inches square , with 3 inches of peat in the bottom and my breeding birds have no problem in climbing in and out,as for the biting this is normal all Parrot like will do this as part of them preparing a nest hole

If its a store bought then the entry whole is standard and the box would be big enough

but if you either did it yourself and did not go by a real layout plan then either the whole is

too small, ( yea i know they are biting the hole that's normal not to worry

if it looks like she is having trouble getting in in would not worry unless she keeps falling

off and down on her butt, these birds don.t have those feet for nothing,

they will play around for awhile and may even appear to abandon the idea

she will get in and you can tell by the frequency of the trips in and out,

The hole in my boxes are about 3 inches square and I use a ladder on the inside made from a piece of wire mesh,but you can use strips of wood nailed across.You do not want a perch poking through on the inside.Put about 4 or 5 inches of peat--rough sawdust--or wood shavings in the bottom and you should be o.k.I always use rough sawdust.Do Not use Pine.You can get packs of sterilised sawdust from pet shops.