Formaldehyde (37%) storage
In the cold some paraformaldehyde (formaldehyde polymer) or trioxymethane (a cyclic condensation product of three formaldehydes) may precipitate. 
It will depend on how much methanol has been added to avoid the polymerization products. 
Normally it will contain 10 to 15% methanol. 

In reality, it is not necessary to store formaldehyde solution in the cold.