I have a Harman Accentra Pellet insert and have been very happy with it until I found rust behind the left hand side of the heat grate/exchanger. The unit is just 1 year old. The dealer who installed it came out and said NO water is not coming in from behind it. He didn't have any explanation on what caused this rust. The stove is vented through the chimney. Any ideas on why/what casued this corrosion problem on the left side only? Thanks.