[sourdough]

open the compartment and look what might be in there. I use a flashlight. May be some sort of blockage. I know my S&B hwhs blow back a lot of flame when they ignite and that's why they all have a shield on them at the entry point. Would it be that simple? Have you seen the flames before or is this just a happenstance occurrence? I also have bug screens installed over the exhausts of my heating appliances.