HP Officejet 5610 – printing multiple pages

The printer is printing blank pages within documents, that is, the printer is picking up blank papers.

Having consulted my A+ troubleshooting guide :), I checked:

The printer is quite new so I doubt it’s due to equipment at this stage. In any case nothing seems to be worn out.

How do I check if this is due to humidity? Any meter that I can put in the room?

The thing is I wouldn’t be aware since I’m used to the room.