Hello Sophie, I had the same problem. My Harman took 8 full nails, 3 heads and a couple of stones before I noticed them in my weekly stove cleaning. I put 15 bags through the XXV that week. After that, I sieved the pellets by rolling them down a channel over a strong magnet. It was a real pain but I found some nails and other random metal before I put the pellets in my stove. I did find some metal in the pellets. They were really small pieces as everyone is saying a nail could not get through the mill whole. The supplier exchanged 2 tons of the unused pellets with new pellets, The manufacturer stopped taking to me even after I sent them the following picture… I think that JustWood hit the nail on the head as to the source but that does not help your stove. You could make a separator. All you need is a U-channel put some strong magnets on the underside of channel . Put it at a 45 and slowly pour the pellets down the channel into a bucket. This is a pain or you could sell them to a random victim on Craigslist.